An altar is a place specialy set aside place for religious and magical workings, as the magical dictionary says. To set it up, you must know the basics on what to have on it.
Altar Cloth- If your altar is made out of wood or glass, this is useful. It will help the objects you put on your altar from scratching the wood, as extra negative energies may keep what your doing from being successful.
Altar Pentacle- A symbol. You can draw one on a piece of paper. Or use a cloth with your symbol on it - the cloth with the symbol also can solve both the altar cloth and altar pentacle.
Candles - It is recommended to use silver and gold candles. But so it won't cost you an arm and a leg, use white. But use diffrent colours for a special sabbats.
ROE - Representations of the Elements. May each symbol represent a element and mean something to you.
Water- A shell, water, rain water
Fire - Open flame, red candle, white candle, lava lamp
Air - Feather, incents
Earth- Rocks, stone, sand, herbs
ROGAG- Representations of the God and/or the Goddess. These can be statues or candles with colour for the representation of the god or the goddess. Athame or Wand - You use this to cast the circle. I hope this article was any , if not completely helpful or informational.