Assemble a basic altar is really quite simple. Probably you will want to include some other things to decorate it, but most importantly in principle is to be functional. It has to be created with the idea to help you reach your goals. Let's look at the basic things involving most of the traditions of Wicca and Paganism in the altars.
The Altar for MagicGet the symbols of the four traditional elements. These are usually aligned to the four cardinal points. You can put a container of Earth or sand at the northern end of your altar to represent the Earth, a stick of incense in the East can symbolize air, a candle or coal in the South to fire, and a bowl of water in the West.
Candles: You can add on your altar also a candle of the Goddess and one to God if your tradition refers to them, or you can use four candles to represent the four directions. Be sure to always have a lighter or matches.
The athame: Most Wiccans and pagans use a dagger in its rituals, so you can put one on your altar.
The wand: The wand is used for direct energy, so if you decide to use one, keep it on your altar.
Your book of shadows: If you're going to make several spells or rituals, it is useful to have one on hand. Basically, it's a diary or personal recipes where you keep the spells that you use, takes notes, and documents your experiences and results.
Spells for Beginners
You can add other items as needed, and space will allow you. You can include any components that you will need for your spells. If you are celebrating a special occasion or, invoking a particular deity, you can decorate the altar accordingly also. In any case, make sure that your altar contains everything you need to make effective spells before the ceremony.