(If you don't know about the magic ring, here is a good tutorial.)
Pull your ring closed and then slip stitch to join.
Chain two. This will count as your first half-double crochet. Make another half-double crochet in the space under the stitch, between posts. This will give the yarn a tighter weave. Make two half-double crochets in space under the second stitch. Make one half-double crochet in the space under the third stitch. Repeat the pattern all the way around the ring.
Join in the front loop of the final stitch with a slip stitch. Then chain 3.
Now in the back loop of each stitch, do one double-crochet all the way around. You should end up with a little cup.
Pull the yarn from the magic circle tight and then tie it and your other piece of yarn together.