To begin, loop the end of the yarn (the "tail") behind the yarn coming from the skein (the "main yarn") to form a circle like this:

Hold the loop where the yarns cross, like this:

Bring the hook through the front of the loop to grab the main yarn:

Pull the stitch through to the front of the loop:

Now chain the number of stitches you need to start your pattern (in this case 3 chain stitches will form the first double crochet):

Continue to work into the loop, crocheting over the tail, until according to your pattern, you have finished the round:

At some point, you can pull the tail nice and tight, and the center ring will close together beautifully!

Make sure to weave the center tail in very thoroughly to secure your loop!