These MOSFETs are configured to give a behaviour close to that of a BS170 discrete MOSFET. The left MOSFET controls an LED circuit, and the right MOSFET controls current through a 5 V DC motor. The top voltage supply represents V_DD, and the bottom voltage supply applies V_GS to the MOSFETs (the sources are grounded, so the gate voltage alone determines V_GS). This could also represent a digital output of a mocrocontroller, where '0' = 0 V turns off the LED and motor, and '1' = 5 V turns them on. Note how no DC current is required at the transistor gates, meaning that they don't load the microcontroller output. Now you can control devices that require currents larger than your microcontroller can output!
