The TIP120 is an NPN darlington pair - ie a bipolar device, not a MOSFET.
MOSFETs come as p-channel or n-channel.
You have the wrong circuit for your TIP120, you must low-side switch a load with an NPN,
not high-side switch - you have an emitter follower circuit, in which the emitter voltage follows
the base voltage (less 2 diode drops).
So emitter to ground, collector to LED cathode, LED anode to +ve supply (with suitable current
limiting resistor in series).
And the base connects via a 1k resistor to the controlling pin. Because darlington pairs have a switching
gain of about 1000 a 1k resistor is usually fine for any load.
A darlington pair is an arrangement of 2 BJTs (bipolar junction transistor, or just "transistor").
MOSFETs are completely different in function to bipolar devices, then respond to an electric field produced
by an insulated gate electrode - no current flows in the gate at steady state, the device is voltage
controlled. You cannot interchange the two types of device.