Take a look at Input.GetKey and Input.GetKeyDown
answered Nov 17 '11 at 01:28 AM
Check out the Input Manager:
Edit -> Project Settings -> Input
After choosing this from the menu, look in the Inspector.
You'll see an item named Axes, which can be expanded and edited.
This is where all the inputs (and their behaviors) are defined.
answered Nov 17 '11 at 02:31 AM