Most of the time when you want to do a
spell or a
ritual, you will want someplace to put your
tools, your
inspirational items, anything you use to help you. Sometimes you also like to have a more
permanent place in your house somewhere that is dedicated to your chosen deities. I will explain a little of both types of
altars and what you might put on one.
Permanent Altars
A permanent (or semi-permanent) altar is usually a somewhat out of the way, squat table where you put inspirational/devotional objects. They can be simple or very complicated; I prefer something in the middle. First of all, you'll want to choose a pleasing type of table. I don't have much choice in the matter seeing as how I have very limited space and money, so my altar is atop my corner coffee table. I don't think deities mind being honored on a cheap coffee table, especially since I don't think of Them as "people" but as forces in the universe. In any case, I do honor Them with my altar, just as an acknowledgement of my appreciation for being alive and for being blessed as I am, and as a reminder that I am always learning about the mysteries and learning to further understand life.
You should face your table to whatever direction you desire, some say the north and some say the east. There is the question of whether the altar should face in your desired direction or whether you will be facing your desired direction when you stand in front of it and look at it. That is up to you! Most people wish to be actually facing the direction they choose. Remember that the north is associated with Earth and the west is associated with Water, both feminine/Goddess-related; and that the east is associated with Air and the south is associated with Fire, both masculine/God-related. If you prefer one direction, you should make sure your altar faces (or that it stands so YOU can face) your desired direction.
Cover your altar with some sort of cloth if you like. This can be appropriate for the season or just be a cloth you like or a cloth covered with a design that inspires you. An altar often changes a bit with the seasons (as the Earth does!); in the fall it might have gourds and pumpkins, pinecones, and fallen leaves decorating it, while at other times it might have fruits of the seasons, seasonal flowers, and so forth. These things are only background, though, to help put your altar in the right "mood." What goes on the altar as more than decoration is the most important.
First of all, most people like to have something representing the object of their altar! That would be, for most Wiccans and Witches and general Pagans, the God and the Goddess. (There are some traditions, such as the Dianic, that worship and use the energy of only the Goddess, but they are not the majority; most people like to acknowledge the God and Goddess as like a duality of nature.) Usually the left half of the altar is dedicated to the Goddess, while the right half is the God. Some objects that express both or are "androgynous" might go in the middle. Some people use images of the God and Goddess (Goddess images are often little clay women, mother figures, or other female "idols," while the God images sometimes take the look of powerful man-figures, animals with horns, or just the horns). Some people use something as simple as a round stone for the Goddess and a pointed or tapered stone for the God. But I think most people probably use candles. White, green, or silver candles are often used for the Goddess, while black, red, or gold candles are often used for the God. I find that the colors red and green flip-flop a lot in representation; green can be the color of the Goddess but still represent the God in His adult form, while red can be the color of the God but still represent the Goddess in Her Mother form. I like this "ambiguity" because they are not two sides of the same coin; they are really more intermeshed than that. Duality exists but let's face it, men and women are quite a bit the same as well, and our concepts of deity should reflect that in my opinion. So anyway, a Goddess image on the left and a God image on the right work nicely.
What else? Often the altar is decorated with tools or objects, arranged as symmetrically as possible with the correct tools on the correct sides. (And by the way, a ritual altar is more often complicated than a permanent one.) Besides my God and Goddess candles, I have a round rose quartz on the Goddess side and a pointed rose quartz on the God side. In front and center I have an incense burner. On the Goddess side I have a small bowl. Sometimes I pour sunflower seeds (occasionally other things) into that bowl on the altar and later toss them outside. On the God side I have a small bowl that holds my matches for lighting the candles. I have a bell on the Goddess side and a small knife on the God side. I have a little clay mother type figure on the Goddess side and a small clay animal whistle thing on the God side. And on the God side I have my wand leaning up against the altar, while on the Goddess side I have my besom. Finally, in the back and center of my altar, I place seasonal items--this is up to you what you want to put there or if you want your altar to change as the wheel turns.
I'm going to be vague on what goes on a permanent altar because it is somewhat personal, being that it becomes a part of your décor in your house and really represents what you want to do (like most things in Wicca and Witchcraft!). But just try to put things on it that make sense to you: inspiring images, things that make you feel closer to the mysteries, things that make you happy, things that you wish to "offer" to any gods or energies you believe exist (I know of some who put food out for the little people!), or even things that you wish to become blessed. Because much of the time, at least once a day, you will use a permanent altar to concentrate solely on honoring the deities or pondering the divinity within yourself. This is what I like to do: before I go to bed, light the candles and sit down in front of the altar, watching the candles and writing in my journal. It is a nice way to complete the day and a good way to put peace inside yourself for a good start the next morning. You can light some incense and pour a little bit of food or even wine or fruit or whatever into a bowl to sit on the altar. After a while, your entire table full of "stuff" becomes a sacred place, just a nice positive space that is a great reminder of your goals and your beliefs. Have fun with your altar and change it however you see fit!
Ritual or Spell Altars
These, as mentioned, are a bit more complicated because you are actually *doing* things with materials instead of simply contemplating them in most cases. You should use a small table or any surface, including the ground or floor, for your altar inside a circle. It goes at the center and generally faces the north (because that's the Earth direction and is generally associated with power), sometimes it faces the east (because the Sun and Moon rise there and they are really GIANT symbols of the God and Goddess). Again, it is covered with an appropriate cloth and the left belongs to the feminine energies while the right belongs to the masculine. You should have on it, again, symbols of the God and Goddess if that's who you honor (and who you want presiding over your rituals). Sometimes the elements are represented at the north, east, south, and west sides of your table, and sometimes they are places at those quarters of the circle. I prefer them on the circle instead of right in the altar, because lots of manipulation usually goes on on the altar and I would not want the elements to be there if they did not need to be manipulated during the spell or ritual.
After you have whatever desired God and Goddess symbols at the right and left of your altar (respectively), you should fill in the rest of the altar. This will change depending on what you need. Most rituals and spells will involve several tools; the athame, wand, chalice, and pentacle are some of the common ones. You should also keep in mind that some rituals and occasional spells involve consumption of food or ritual beverage; don't forget these! I especially like to use apples, and those go in the middle and are cut later on the pentacle or just a plate. Wine or juice can sit pretty in a chalice on the Goddess' side, while a bowl of corn or nuts can decorate the God's side. It depends on what you are celebrating. More specific information about types of food and tools for certain celebrations is included in the Pagan holidays writeup.
If you are doing a spell, the middle of your altar should have your spell materials, in between the tools and images that represent each deity. If you are doing a candle spell, you should have the candle in its holder, a crystal for inscribing whatever symbol, and a piece of paper and an ink pen to write whatever you will burn . . . well, if that is the way you are doing your spell, that is. If you are doing a ritual to honor a person who has died, you might have the person's picture there. If you have made a small ceremonial wand, are creating something important by candlelight, or are blessing a charm of some sort, all that you need should be to the front and center of the altar so that you can work with it.
Everything you put on your altar should serve some sort of purpose, whether it is inspirational or functional. You should never just stick a cup on the Goddess's side just because you read somewhere that you should; never use a symbol without knowing why it is there, or it just takes up space and is really sort of offensive. ALWAYS make sure that you know why you are doing something, or it will be meaningless to you!