3-pin MOSFET: P or N type?
Assuming that is is an enhancement MOSFET (most common):

If it becomes conducting if the gate voltage is some volts higher than the source or drain voltage it is a N-MOSFET.

If it becomes conducting if the gate voltage is some volts lower than the source or drain voltage it is a P-MOSFET.

It is very likely that there is an internal protection diode (there are only very very few MOSFETs without them; at least if it is a power MOSFET).
You can use it to find out which pin is source and which one is drain:
P-MOSFET: anode is connected to drain, cathode is connected to source
N-MOSFET: anode is connected source, cathode is connected to drain.