The three wires in any typical household circuit are your Ungrounded Conductor (hot wire), Grounded Conductor (neutral wire), and Equipment Grounding Conductor (EGC/Ground Wire). The hot and neutral are what actually makes the circuit work. The EGC/ground is a safety measure that creates a ground fault current path which enables overcurrent protective devices (like breakers and fuses) to operate.

As far as learning common electrical, I'm sure local organizations in your area will have some kind of classes. Probably local hardware stores? I don't know. I learned through trade school and on-the-job training. As an electrician, I will self-servingly tell you that you should always hire a licensed electrician.

> The EGC/ground is a safety measure that creates a ground fault current path which enables overcurrent protective devices (like breakers and fuses) to operate.

This is NOT TRUE!! You've said it so many times in this thread, and it's just not true.

A lot of people are tying to correct your mistakes, but you're not fixing them. Please do so, you are misleading a lot of people.

Perhaps you could explain it correctly?

You can trip a breaker without the ground wire being involved. The ground wire does help with one failure case, but that's not the only way that your circuit breakers/fuses protect you.

Are you thinking about 240V circuits which used to use 3-wire circuits but now use 4-wire? The US run split-phase power to homes with +120V and -120V hot legs and neutral connected to center tap of transformer. Each 120V circuit uses one of the hot legs.

For 240V, can use 3-wire circuits by getting 240V between the +120V and -120V legs. There are 3-wire grounded plugs (hot-hot-ground) and non-grounded (hot-hot-neutral). Modern 240V wiring uses 4 wires, hot-hot-neutral-ground, which allows making 120V for low-power electronics from one hot to neutral.

It's not safer, it's more useful. You run out the hot, neutral, and switched hot. That lets you use a light switch to control an overhead light/fan without killing the fan.