You'll need, the aforementioned encoder, 22 guage wire (I think that's the right guage), and some quick-disconnect connectors for 22 guage wire, and wire strimper, and a crimper.
I went to radio shack and said, "I need all this stuff," and the guy just picked it all out for me.
As for wiring, each button will have a microswitch attached to it, and each joystick will (usually) have 4. They look like this:

Each one has three prongs, but we only bother with two of the three: the COM prong, and the NO (normally open) prong (guys, correct me if I'm wrong). To connect wire to the prong, you'll use a quick disconnect:
(see #4 in this pic):

To add a quick disconnect to wire, you strip some of the insulation off the wire, and insert it into the quick disconnect, then you use a crimping tool to secure it in place. Each little quick disconnect connector that you crimp slides onto the specified prongs on each microswitch.
there is a spot on the encoder that says "com". You twist the screw up on that, insert some wire, twist the screw back down, and then make a chain of connections from this spot to each of the "COM" prongs on each of your switches. This is your ground. It's a "daisy chain."
Then, for each of your buttons, you take a length of wire and connect it to the proper spot on the encoder, then crimp the other end of the wire w/ a quick disconnect, and put that connector on the "NO" prong on the microswitch (it's usually labeled).
does that help any?