Crocheting in the round is one of the fundamental skills of creating amigurumi. In order to begin, once must create a circular foundation. There are two primary methods for doing so. These are the magic ring and the chain method. Personally, I prefer the magic ring. I find that it looks nicer and it is also easier to form a larger number of foundation stitches, sometimes necessary for a larger project.
The following video details how to begin using both methods. Try both and see which one works best for you!