This is up to you. Any flat surface will do, whether it's a table, desk or shelf. Many people like to have it in a quiet area of the house, but some do prefer to have their altars right out where all the daily action is. If you are a bit of a kitchen witch, you could have an altar right on the counter, for example. It's your call.
Wherever you put it, make sure everyone in your home respects it. If it's out in the living room, you don't want it to become the spot where the TV remotes go or your children's homework piles up. Your altar needs to be treated as sacred space, no matter where it is.
If you aren't comfortable having your altar out in the open, you may need a few tips on hiding your altar. Not everyone is comfortable with witchcraft, so be discrete if you have to be.
What Goes on It
Again, that is pretty much up to you. A typical Pagan altar display usually consists of a few traditional tools, but you can interpret this however you like. Basic altar tools include:
A ritual knife, or athame
Chalice or goblet
Besom, or broom
Statuary representing Deity
Bowl of earth or salt
Decorative items like feathers, plants, crystals
The tools you choose to keep on your witchcraft altar should reflect your own personality and style of witchcraft. If you like to cast candle spells then have an altar filled with candles.
You can also store your Book of Shadows on your altar as long as you don't mind that people may pick it up and even read through it. Most people prefer to keep their BoS in a less public location.