The first thing you need to learn the following coin-trick is a coin.
I'm happy to hear that you liked my joke, but it's time to get serious: this is the coin I will use. It is a coin representing one 'cent,' from the U.S.A.:
Obviously something horrible happened to it at some point between its minting in 2005 and our current region of time, otherwise it wouldn't have all those stains or whatever. Now let's move some metal.
Step one is easy: give your knuckles a workout I call the talon-izer, or alternatively the talon-ator. Either name is acceptable: see which one works best for you.
Step two: Make sure with the audience that they're okay with you casting what amounts to a spell on them. The universal sign of the okay is all it should take, but make sure to do it with the coin so the audience knows that it will be involved:
Step three: If you are going to traipse down the path of the coin trickster, you'll probably hear the following aphorism/rule-of-thumb at some point: "before you re-knuckle, remember to de-knuckle." If you can't tell, that's exactly what's happening in this image:
Step four: pass the coin--in my case, the pictured coin, from your third to your fifth knuckle. Be sure you've made suitable arrangement beforehand so that your audience is not directly in front of you:
Step five: Enough with the knuckles already. House the coin in the webbing of your second and third fingers while you prepare for the great disappearing act:
Step six: You're going to go ahead and need to shout 'Abracadabra,' or, 'Hocus Pocus,' depending on whether you've de-knuckled yet. Suddenly, where's the dang coin gone?
Step seven: There it is!
Amaze your friends/bore your enemies