With an NPN mosfet, the Source is connected to "ground" 0 volts, and the Drain is connected to the load. The other side of the load (lamp) will be connected the positive rail.

The gate connects to the PIC pin with a pull down resistor. I normally use a 100K.

Check the gate saturation voltage if you plan to run the PIC at a lower voltage than 5.

If you are needing switching speed, you may want to look at IGBTs. Some mosfets are pretty slow if PWM is the goal.