Automatic circuits work on the philosophy that some external/automatic switch turns power on and off to a circuit. This can be a photocell or timeclock that controls a set of relays or contactors which allow or disallow current to flow in a circuit.
For those of us that are more visual learners, I've made this show one that can be followed visually. In this episode I draw out on the white-board how switch loops work, and how to wire them.
This episode goes further in depth on how 3-way and 4-way switches work. This is for those visual learners out there that need the logic drawn out so they can see the whole circuit in front of them.