crochetme.com had a
whole issue on it. Its really as simple or as complicated as you make it. I tried to make one recently but... well I made it too complicated and ended up frogging it

Its pretty easy to learn how. You only use a couple skills - single crochet (sc), crocheting in the round, a special "
amigurumi double ring", increasing, and decreasing.
If you've got a hook handy, I'd follow a tutorial on
chaining,
single crochet and make a little swatch, then practice increasing and
decreasing your rows. Once you've got that, check out the
amigurumi tutorial on crochetme
I had a little fun with adding links there

Hope they're helpful