I'm in school to become an Avionics Tech, but I havn't gotten that far yet...

I agree that the schematic in the POH it a bit too complicated for an introduction to the electrical system. The way I'd go about explaining it is simply to say the the aircraft (typically) has two power buses. The main bus powers aircraft systems such as flaps, stater, and fuel gauges. The avionics bus powers the radio stack. Then I'd explain that the main bus is powered by either the aircraft battery or the engine-driven alternator (tie conversation to the two sides of the master switch). The avionics bus gets its power from the main bus via the avionics power switch. The last thing I'd introduce would be the circuit breakers between the bus and the actual device for protection and isolation.

You can make a simplified diagram to illustrate this. Draw two rectangles labeled main bus and avionics bus, connected by a switch. Then on one side of the main bus show the battery and alternator as feeding the bus. On the other show the devices that take power from each bus (with a breaker between the bus and the device). You can use arrowheads to indicated the direction of "flow".

While not schematically accurate, this is functionally accurate and a lot simpler to grasp for new students at first. Once they've got this down, then you can fill in the details.