I have had a few questions as to exactly what they mean, even though I explain it in my arm exercise descriptions.
Pronation is the rotation of the arm so that the palm is facing away from the body. Here’s how to do it:
Do the classic “make a muscle” thing with your arm. Now rotate your palm away from you. This is pronated.
To supinate your arm, simply rotate your wrist so that your palm is once again facing you:
Easy as pie, right?