Hi MaidenCrow, Sorry, but there is no Forum specifically for those who are new. But we'll try to answer any questions you have that you might post, no matter what Forum it is in.
In answer to your question let me start by saying that in my experience circles serve two purposes:
1. The circle helps to contain the energy that you are raising to do a magical working until you are ready to release that energy at its intended purpose. You might sometimes find this referred to as "Raising a Cone of Power".
2. As Brysing said, the circle is also a barrier between yourself and any negative entities or energies that might be attracted to your workings. A circle is a good idea to protect yourself if you are meditating or doing astral projection.
So there are very good reasons for casting a circle when you are doing a magical working, meditating, doing astral projection, or any other time you feel you need protection or you are working at raising energy.
Is a circle always necessary? In my opinion it is not. For instance, if I am cooking dinner and wish to push a bit of energy into the meal for health and well-being I just do it without putting up any sort of circle. Such minor magics generally don't require circle work.