Go to your local bookstore, if you have one, and look in the sports section. There's a couple good bowhunting books out. There's good instructions on tuning at www.eastonarchery.com.
You'll also be able to select a properly spined arrow shaft size there, which is crucial. Ithaca gave some good advise concerning distance. If you're able to attain good shooting form, you'll be deadly accurate at 20 yards in no time at all. Read up on archery and bowhunting all you can, try to go to a pro shop where you can shoot different bows, and select the best one in your price range. If you're gonna shoot fingers (which you should IMO) your choices of compounds is going to be severly limited.