To quote: "A current mirror is a transistor circuit that regulates current through a load resistance, the regulation point being set by a simple resistor adjustment."
For the MOSFET current mirror, the fundamentals are the same however you need to be familiar with the analogies of BJTS and MOSFETS to use the above AAC section. The wiki on current mirrors will give you an appropriate insight: http://en.wikipedia.org/wiki/Current_mirror
The difference between a PMOS and NMOS current mirror is that in one implementation p-type MOSFETs are used as the active devices for mirroring and in the other implementation n-type MOSFETs are used as the active devices for mirroring.
I would suggest that you read the above articles and post back with specifics if you require further help.