When doing any sort of trick there are different stances you do. The 4 different ones are regular, nollie, switch and fakie. Each is different and can depend from time to time, on which foot you may use to pop it into the air and which direction you are comfortable riding. 

 Regular would just be when you are riding in the way you are most comfortable and popping the board with your back foot, while nollie is the same just using your opposite foot. Switch and fakie is when you decide to change to the way you don’t usually prefer.  When doing a fakie is when you are riding your non preferred direction and using your front preferred foot and switch is doing the same thing but with the opposite foot instead.