Riding one footed on a unicycle is just a trick so it has no use other than impressing other nerds and being fun to do and learn.
Step 1: Getting Started
To start, ride in a straight line down a slight down hill road (do not do this in the grass) once you have some momentum test which foot you would like to take off the pedal by slightly lifting it on the up strokes.
Step 2: Riding One Footed
Once you have chosen a foot to take off the pedal go back to the top of the hill and start riding down, after 2 or 3 pedals take your foot off completely. Once your foot is off the pedal you need to keep your momentum up otherwise you will stall. To keep up your momentum you will need to do some special pedaling this means push hard but not to hard on the down strokes and take most of the weight off on the up strokes.
Step 3: Becoming Proficient
Once you can keep your balance, keep your momentum up, have the timing down, all you need to do is practice a lot.