How to crochet a granny square. More specifically the double-chain part...!?

I'm trying to teach myself to crochet. I REALLY want to learn to make granny squares. I can cast on, chain a few stitches, and then slip stitch them to form a circle. I'm lost on the next part. I think I can figure out how to double-chain but I have NO idea where I'm supposed to be inserting the hook. It always says, "double-chain into the circle" and that is not helpful...there are a lot of places I could put my hook in the circle! Could someone clarify? A picture showing exactly where I should be putting the hook would be AMAZING and would be greatly appreciated! Thanks!