There are two types of normal stances which vary from person to person:
Regular -- Left foot forward Goofy -- Right foot forward
You should use whichever seems more comfortable to you.
Once you have decided which is your normal stance, you will also know what your SWITCH, FAKIE, and NOLLIE stances are.
To determine what your fakie stance is, you should be farmiliar with your NORMAL stance.
THEN, all you have to do is get in your normal stance and ride backwards.
In this stance you would assume the opposite postition of your normal stance. Therefore, if you were REGULAR you would have your right foot foward instead of your left, and if you were GOOFY you would have your left foot foward instead of your right.
You ussually don't use switch stance until you have reached a supreme level in your normal stance (regular, goofy). Then you can re-learn all the tricks you have already leared. Then you could do something like a, "switch kickflip", or a, "switch ollie".
The nollie stance is a combination of the FAKIE and SWITCH stances. Put them together and you have NOLLIE stance.
The name "nollie stance" was derived from the trick invented called the nollie (the fakie, switch stance ollie). Then it was realized that any trick could be done this way. So they made a stance.
As a result we got nollie flips and nollie 180's galore.
The quick way to get into a nollie stance is to get in your normal stance and scoot up to the front of your board.