The Altar. This is the center of the circle, the place that the celebration revolves around. The things that are needed are here, either on the altar, or placed underneath it, where they can be easily reached.
Each of the four elements is present, both in a real and in a symbolic form. Air is present in the incense, and in the Athame. Fire is present in the incense as well, and in the wand. Water is present in it's actual form, and as the Chalice. Earth is present in the salt, and as the Pentacle.
There should also be a flame on the altar, usually in the form of a candle. All that is really necessary is a representation of each of the elements and a flame; but lots of other things usually wind up there, too.
Traditionally, things can only be placed on the altar, or removed from it, with your strong (dominant) hand. This may cause a bit of picking things up with your right hand, and transferring them to your left; but you quickly get used to that, and it's a form of respect that reminds you that you are dealing with holy things here, and not your ordinary stuff. As such, I recommend this practice.
This is a representation of the things that you can usually find on our altar. Different traditions use different things, and we use different things for different celebrations, for instance, we might also have a cauldron here. If you want to know more about a specific tool, just click on it.