Mosfets

N channel MOSFETS need a gate to source voltage in order to turn on. This essentially means there needs to be voltage at the gate in order for the MOSFET to turn on, due to the fact that normally the source terminal on an N channel MOSFET is set to ground.

P channel MOSFETS gate voltage needs to be less than the source voltage terminal in order to turn on. This allows the drain to have an inherent voltage of its own as needed.