The manual is a trick that you can get started learning right away, without even having pegs on your bike. In addition to being a cool flatland trick, it's commonly used in other disciplines of BMX, such as park and street riding.
There are a fair amount of manual how-tos on the web, but this example from Extreme Team X is one of the better ones that we've come across. Dig the British accent, and how he calls your butt your "bum."
In this clip for Expert Village, Garson Fields offers some tips on riding out your manual for greater distances: