Altars are a pretty common theme throughout the religions of the world. Everybody's seen the altar up the front of a church or temple, but for followers of many religions it's normal to have an altar in their home - dedicated to one deity or a group of them - usually constructed according to tradition. As a Witch, you get to design your own.
So what is an altar?
The word 'altar' comes from the Latin altare (literally 'altar'), which is probably related to another Latin word, adolere ('to burn'), giving a meaning like 'burning place' - a place where religious offerings are sacrificed. It is generally a flat surface, like a table, the top of a chest of drawers or even a flat rock in the backyard. You can think of your altar as your workbench - it's where you prepare your ritual equipment (herbs, candles, etc.) and also where you perform the actual ritual, so it needs to be big enough to allow you to fit all your equipment on the surface and still leave you a space to work on. Whatever surface you decide to use for your altar, remember that an altar is an area reserved exclusively for ritual and magick - you don't leave your empty coffee cup on it on your way past like the kitchen bench, and it should not collect paperwork like your desk! Your altar serves a similar purpose to the one in your local church, and no priest would be caught dead leaving their empty coffee cup or unopened mail there!
Your altar doesn't have to be permanent - if you're still in the broom closet and want to stay there, for example, then you can certainly put together and take apart your altar as often as you need to. But, if you can leave your altar set up even when you're not actually using it, then it serves a second purpose - it becomes a shrine to the God and Goddess, and a means of honouring Spirit without you even having to be there in front of it.
Where should I put my altar?
There are a few considerations when deciding where you'll put your altar. Firstly, you should decide whether you want it inside or outside. Most Witches, for convenience, put their altar inside; it's more private, it keeps you out of the weather and you can leave your altar permanently set up if you want to. Many Witches would love to work outside, but circumstances usually end up putting them inside.
When you've decided whether you're going to put your altar inside or outside, you now need to decide where in the room you're going to put it (if you're inside) and which way you want it to face (relevant whether you're inside or outside). The place your altar occupies can be determined by what you want to do in your ritual - if you've got a group of people turning up, you may want to put it in the middle of your circle (and thus the room) so everyone can physically gather around it. If it's just you, you can put it against a wall (if there's space) or in the middle of the circle if you'd like to work all the way around it. The middle of your circle is the place with the strongest energy, so that tends to be a popular place for the altar to go.
The direction your altar faces (north, south, etc.) is more important to some Witches than others - generally, North is the choice direction, being (in most traditions, anyway) the direction corresponding to the element of Earth. If not North, then the next most popular direction is East. It really depends on your trad.
What goes on a Wiccan altar?
There are some things that are mainstays of the Wiccan altar, even when you're not setting it up for ritual. Some people also keep their ritual tools on their altar, but I'm not a fan of leaving my tools out to collect dust. Even though I don't leave my ritual tools out on my altar, since I'm a fan of Fire, I tend to always have a few nice candles sitting on it.
When you're setting up your altar, remember that it is a workspace - don't make it so crowded you can't work, and don't put lit candles near the front where you can set your sleeves on fire with them!
Altar cloth
Your altar is a flat surface, and all flat surfaces quickly collect dust and and dirty marks (like drips of candle wax). The Wiccan solution to protecting the surface of your altar is to cover it with an altar cloth - generally a non-flammable material that will protect whatever your altar is made of. If you need to, you can easily take the cloth off, use your iron and some absorbent paper to clean up the wax and throw the cloth into the washing machine. This serves a few purposes - you don't have to scrape up that spilt candle wax and scratch your altar doing it, and it's nice to keep the centre of your spiritual focus - and your shrine to the God and Goddess - clean and tidy! And your altar cloth can be a nice thing to look at, too - if you're handy with a sewing machine, you might have different cloths for everyday use, for each sabbat, and for esbats. They can be quite pretty things, with relevant symbols or pictures embroidered on them (here's where high school textiles classes come in handy). Even iron-on transfers and embroidered patches from your local Spotlight can be used - make your altar cloth whatever you think is appropriate. Black and purple materials are common, but you can use whatever colour you like.
God/Goddess images/symbols
Because your altar is the focus of your spirituality, it's important that you have something representing the God and Goddess on it. These things are any objects that you associate with the Divine - perhaps actual statues/drawings/images of a God and Goddess, or gold and silver candles, or even flowers. Personally, I have a framed picture of an orange tiger laying down and resting its head on a white tiger laying in front, against a background of grass and trees - this just appealed to me as a representation of the God and Goddess. If you're looking for something more conventional, I've compiled some image galleries of God and Goddess images you might find helpful (it'll save you trawling though Google image searches).
Elements
It's also important to have something to represent each of the four elements on your altar, because they basically represent the building blocks of the Earth. You might use salt or sand to represent Earth, a feather or incense for Air, consecrated water for Water, and a candle for Fire. You get the picture.
Pentagrams/Pentacles
You'll find a pentagram or pentacle on 99.9% of Wiccan altars. This isn't necessarily because people know why they're putting them there, but because they figure the pentacle is the symbol of Wicca and they should have one on their altar. This isn't strictly true - the pentacle is the symbol of Wicca, and you should definitely have one on the altar; but you should realise that there is a reason the pentacle is the symbol of Wicca and that this reason should be why you've got a pentacle on your altar. There's a nice intricate explanation for you :)
So, the reason you would put a pentacle (or pentagram) on your altar is because of what that pentagram represents. It generally symbolises the four elements (the four lower points) connected with, but ruled by, Spirit (the uppermost point), while the circle in the pentacle symbolising eternity and the cycles of life and nature. In addition, the pentagram/pentacle is a powerful symbol of protection and can be used to banish negativity. Why wouldn't you put one on your altar?
