There are several different types of service, but the two main ones are Rite 1, with more traditional language, and Rite 2, an expanded service with more modern language. There is technically a Rite 3, which is a nickname for a looser liturgy not to be used on normal Sundays but for special occasions or as a starting point for a custom service.
A church will sometimes offer a stripped down Rite 1 without music, choir or hymns first thing in the morning, and then one or more choral services using Rite 1 or Rite 2. The structure is quite similar, but I'll try to note where these differ along the way.
The day really starts with letting in nice Mrs. Davis, who has been there since 6:45 even though the first Rite 1 service is at 7:45. Whoever's job it is, be it the sexton or verger to open the place, lets her in where she takes her customary position in her favorite pew, while the coffee is brewed and the day's services are arranged.
And there's a lot TO be arranged. The sign-in sheets for acolytes and lectors and Eucharistic Ministers go on the entrance podium, and the quietly nervous waiting for people to show up and sign in begins. Meanwhile the prayers of the People, if not already approved by the Vicar, Dean, Rector or Bishop, go to him or her for final approval. Lights are brought up, candles are lit, vergers don their black robes and wait for people to arrive. Meanwhile the clergy are making last minute adjustments and warming up in their staff room.
The vergers are also quietly on the lookout for people they know are trained in various roles: if the acolyte doesn't show up one of them will throw on a white robe and act as crucifer. If a lector calls in with a flat tire, hopefuly another parishioner who's a lector can fill in, or the priest will be notified he will have to read both lessons.
But if the stars align, and everyone's there and vested: the choir are robed, the ministers are robed, the acolytes are in their albs cinched with rope belts with boxes of matches hidden in their cowls. People are greeted on the way in by ushers and handed any relevant literature for the service, and the verger begins the task of lining everyone up.
If it's a Spartan Rite 1, the order is something like verger, acolyte carrying a processional cross, Eucharistic Minister, then priest. At the 11:15 full bore rite 2 service, it might look like verger, thurifer swinging a metal ball full of smoking incense (on a feast day), crucifer flanked by two acolytes carrying candles, the choir (trying to stay far away from the choking fumes of the thurible), Eucharistic ministers, then priests. With the line-up approved, the service begins.
It can be anything as simple as the verger knocking on the church floor with his or her verge, or the stirring first chords of the processional hymn. As the party files in, some nod or cross themselves as the cross comes past, and then depending on the setup of the altar and seating, the members of the clergy and choir and associated ministers and acolytes file in procession to their assigned places. The cross is held by a bracket on the wall, the choir takes its place in the pews. It's timed so that roughly on the last stanza, everyone's finally in place and ready for the service itself.
Placement, number and timing of hymns may vary: though omitted from this narrative, it is certain that at least two or three hymns outside the processional and recessional and offertory will take place.
The rite opens with "The Word of God", namely an introductory prayer blessing God and asking Him to open the hearts and minds of the congregation. The prayer includes the Two Commandments, sometimes a "Kyrie Eleison" and a closing affirmation that only God is Holy.
What then follows is the "Daily Collect". If the church is one to follow the service in the Book of Common Prayer as opposed to printing it all out in the bulletin, typically this is where the small slip of paper or insert handed out by the usher is followed. It is different each week, and references some relevant prayer for that part of the church year.
Then follows the lessons: typically a layperson known as a lector approaches the front of the church and reads from the Bible, announcing the reading(s) as "A reading from ________". Typically lay persons read from the Old Testament and/or Epistles. What then follows is the priest reading from the Gospel. In the full-blown version of Rite 2, sometimes the priest, complete with crucifer and candle bearers will leave the altar and walk down into the middle of the church itself to read the Gospel in the midst of the congregation, and then return with a processional organ instrumental. This is bracketed by something akin to "The Holy Gospel of our Lord Jesus Christ according to _________" / "Glory be to thee, O Lord" - and "The Gospel of the Lord" / "Praise be to thee, Lord Christ".
At this point a sermon or homily is given by the Sermoner, and in some churches this is the cue for small children to quietly file out to Sunday School. A sermon can be anything from a deeply intellectual textual analysis of one or more of the assigned texts for that Sunday, or it can be a very personal testimony relating to the text. Sermoners can be dry, funny, personal and engaging, or possessed with serious book learning and insightful background notes. However, a bad Sermoner can lead to the twenty minutes or so of the Sermon being some of the longest it is possible for a human being to experience.
The church then recites the Nicene Creed, at the end of it a lay person known as an Intercessor makes his or her way to the front of the church.
In Rite 1 the "prayers of the people" are simply read with a pause between paragrahs. In Rite 2 or in longer versions of Rite 1, the priest calls out for the congregation to recite "Hear our Prayer" at the end of each paragraph. In essence the prayers start off with a prayer for the ministers of the church, bishops, and the Archbishop of Canterbury, as well as the congregation, diocese, mayor, governor, and President.
The prayers then continue with praying for people with immediate concerns or sudden illness or accident, then these people are mentioned one at a time by name. They then carry on to praying for people with long term concerns or chronic illness. And finally, prayers are said for those departed this earth in the faith and fear of the Lord. As an intercessor, it can be sobering to watch a name cross over from "immediate concerns" to "chronic concerns" to "departed this earth" as the weeks pass by. If a family has donated altar flowers that week in the memory of a deceased relative, this is mentioned.
Given that though the Episcopal church does offer a sacrament of Confession, the practice of going into a booth for personal confession and penance is not widespread, at this point in the service the congregation joins in "The Confession" - prayer to confess that in thought, word and deed and by what was done and/or left undone, we have not loved God with our whole heart and our neighbors as ourselves. Prayers of repentance and confession follow.
The priest asks God to absolve all present of their sins, and invites everyone to "the Peace", in which members of the congregation greet each other, shake hands, and engage in some lighthearted although brief conversation.
At this point the priest, being in effect also responsible for practical day to day matters, greets newcomers and reads what amount to "the morning announcements". Given that the tone is lighter, it's the time to remind people of upcoming food drives, or educational opportunities or meetings.
There is at that time an offertory, in which ushers collect cheques and donations of cash by handing brass plates throughout the congregation, while a hymn plays and/or is sung. The offering is then brought to the front of the church and blessed, and then immediately secured "backstage". This is a good opportunity for the head (or only) Acolyte to wash the hands of the priest with water and cloth at the side of the altar, catching the water in a small vessel.
The church is now ready for the main event: Communion.
Either sung or spoken, the priest declares that it is a good and joyful thing always and everywhere to give thanks to God. The events of the Last Supper are recapped and the congregation is reminded that Jesus asked his followers to break bread and share wine together as oft as they are together. This prayer is rather long. At the end, the priest breaks the bread in front of the congregation and pours a small amount of water into the wine and declares them "The Gifts of God, for the people of God."
First, the priest takes communion himself (or the priests adminster it to each other if there are more than one). Then, the Eucharistic minister(s) and Acolytes are given communion. This frees them to take their places as the ushers quietly file the congregation in orderly rows to the altar rail to kneel (or stand in case of infirmity). ALL are welcome to partake in communion. Though in theory it is historically reserved only for those with a trinitarian Baptism, in practice everyone is welcome, regardless of personal belief or baptismal state.
First the bread is offered with a spoken affirmation by a priest with "the Body of Christ, the bread of Heaven." The parishioner is welcome to accept this (or decline by crossing his or her arms in front of him). In the case of someone abstaining from communion, the priest will bless the person instead. The parishioner can either choose to keep the bread in his or her hand and "intinct" it by dipping it into the wine, or eating it and accepting a drink from the chalice of wine. Communion is equally valid by wine, or bread, or both - so alcoholics, those with celiac disease or dietary restrictions may participate any way they wish or are able. The wine is offered with by a licensed Eucharistic Minister or priest with something akin to "The Blood of Christ, the Cup of Salvation".
Once the entire church has been served, the priests typically hold the bread and wine aloft to ask if there are any in the congregation who cannot make it to the altar. They will come out into the midst of the congregation to offer communion to those too infirm to make it to the altar. After this, chalices are covered out of respect and plates are gathered together and moved to a small antechamber outside the main church. Spare wine and/or hosts are either consumed or disposed of respectfully. Many churches have a sink specifically for altar wine that drains into the earth and not the sewage system.
Eucharistic Visitors are given a box containing consecrated hosts and wine, and sent by the congregation on behalf of the church to offer communion to those who are too infirm to make it to a church.
Then, a post-communion prayer is said, in essence thanking God for allowing us to share in the mystical blood and body of Christ. The congregation stands, a recessional hymn is played and sung, and the party that entered to start the service files out - verger, thurifer, etc. just before - and at the end the priest charges the congregation to go out into the world to do what work it is God wants us to.
Priests block the exits and warmly shake the hands of people exiting the service, and depending on the nature of the parishioner and his or her interest in talking a while, this can hold up the lines. Meanwhile the acolytes are shedding robes and replacing crosses, candles are being extinguished, vergers are making sure nobody absconds with the Prayers of the People and/or watching to see who is supposed to be there for the next service. People file into the church hall for coffee and/or sandwiches or even sometimes a small cash bar selling wine, depending on the nature of the congregation and/or local standards and laws.
There is a blessed pause, or lull - and then if there's another service that day, the whole thing starts up again.
TL:DR - Stand when other people stand, sit when other people sit, kneel when other people kneel - you'll do fine!