Handfasting is the ritual occasion when two Wiccans want to be together as in a marriage.
All Wiccan rituals begin with a circle casting. Since we don't tend to have church buildings, and we often worship outdoors, this is how we declare a place to be our church for the duration of the ritual. The Circle may be cast with great ceremony and fanfare and waving of swords, or it may be done simple by gathering the participants in a ring where the ceremony is going to take place.
Then, after the circle casting, there will be a invocation of the four elements: Earth, Air, Fire, and Water in the four directions. This may involve spoken incantations, or it may involve holding up or carrying physical objects which are symbols of the elements.
After the four elements invocation, the priest and priestess invoke the divine forces, in the form of the God and the Goddess. They may also be called under specific names in order to indicate something about the particular quality of divine energy we want to bring into our ceremony.
When the invocations are done, there will be a wine blessing. The priest and priestess (or the bride and groom if they wish) will dip a ceremonial knife into the chalice. This symbolizes the creative union of opposites -- female and male, Goddess and God, earth and heaven, life and death. After the wine is blessed, it may be passed around the circle for all to partake in.
After the wine blessing, the couple will exchange vows, just as they would in a normal wedding. After each has said their vows, the Priest and Priestess will tie a ribbon around the bride and groom's wrists.
When the couple is tied together, they will proceed to leave the circle by "Jumping the Broom" which symbolizes crossing the threshold into married life.