General Idea
A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a transistor that allows current to flow only when enough voltage is applied to it. The MOSFET has three pins, the gate, drain and source. If we have a resistance between the source and drain pins we can power it by applying a voltage to the gate pin. The cool part about this is we can vary the current as we vary the applied voltage. This makes it useful in circuits such as PID Control for Oven.