Wicca & Witchcraft - Altar
Within Wicca, the altar basically performs the same function as any altar in any church does. The kind of things that you use on your altar should very much reflect your own personal beliefs.
You will need to decide whether your altar will be a permanent one or one that will be put away after each use. The size of your altar will very much depend on this decision. We know of altars that are available online that are as little as 6" across. Quite frankly we consider this just too small for any practicable purpose unless you are incredibly short of space. Think about what you will be placing on your altar and that should give you a good idea of the minimum size you will need.
Shape is purely personal preference. Square, oblong, or round. It doesn't matter. Some practitioners like to use a table, some a cupboard style arrangement for storage purposes. The choice is yours.
Most practitioners will opt for an altar made of a natural material. Wood is undoubtedly the most popular but metal, glass and stone also feature. Most would definately agree that something like plastic should not be used.
Most practitioners will choose to cover the altar with an altar cloth. This is not absolutely necessary. It will depend to an extent on what you are using for an altar. If the altar is purpose made (particularly if it's made of natural wood rather than plywood etc.) it seems a shame to cover up that natural beauty. But again, the choice is yours.
It is always good practice to cleanse and consecrate an altar prior to use. Probably the quickest way to do this is to smudge it with sage or wipe it down with (sea) saltwater. An alternative to this is to let the altar be exposed to sunlight or moonlight. It works just as well though takes longer.