Magic Circle - I don't use one often, unless something is truly weighing heavy on my mind or I need added comfort. It's an energy field (so to speak) that you surround yourself with before you begin anything magic (also used before meditating - as I said, a peaceful safe place). A magic circle provides protection since you cast it with the intent of positive energies only being allowed to enter, thus protecting you from negative. It is often said to increase power as well.