How to do a Manual or
The manual is like doing a wheelie. The front wheels are off the ground and the skater is rolling on the back wheels only. The opposite would be the nose manual in which the the front wheels are on the ground and the back wheels are in the air. It takes better balance to pull off the nose version of the trick.
To do the trick you just put your foot on the tail or nose depending which version you want to use. You shift your weight and roll. The painful part is if you lose your balance you can launch the skateboard out in front or behind and bail into a hard landing.