First off, find some interesting looking shells that are thick enough, and have openings large enough, to drill some holes in.
Make your holes as close as possible to the edge of the shell, without breaking it.
Locate the beads that you would like to crochet into the hangers, or, in my case, the tiny shells. Put your beads into a bowl or dish so they are easy to pick up as you are crocheting.
Make a slipknot in your crochet thread and pass your hook through the thread, and then through the hole in your shell. Yarn over and draw through the slipknot to form a stitch around your shell. Draw the thread tight around the shell, but be very careful and pull gently to prevent your thread from being cut by the edge of your shell.
Decide how far apart you would like your beads to be, and count out how many times you chain so that you can space the beads evenly around the hanger. I chained five, then attached my tiny shell. Make a stitch around your bead just as you did to attach your thread to the shell in the beginning. The stitch to attach your bead, and the following chain do not count in your spacing, they are just to lock the bead into place. So, stitch once through the bead, chain once to lock it, then start counting your chain stitches for spacing. Continue until your hanger is long enough to slip over a branch on your tree, then, after your last set of spacing chains, slip stitch to beginning stitch (the one that you used to attach your thread to the shell.) Fasten off and tie the tail from your beginning stitch to the tail on your ending stitch.
There you have it! Put it on your tree! I like to make a set of 5 or 6, using different colors and shapes of shells.