Please Don't Facepalm Me!

Ground is just what it means, the earth basically. Electricity needs to go somewhere, ground just gives it somewhere to go to complete a circuit. If you have and LED (one of those little lights) and electricity has to go through it for it to light up. So the electricity is on one ends and when you put ground on the other then the electricity goes to the ground. Electricity always finds the fastest path to the earth, a battery simulates the ground for somewhere for used electricity to go.

Think about this. Lightning finds the quickest path to the earth, which is why it will strike a tree instead of the ground because solid objects conduct faster than air.
I saw in Bibin's guide for how to frontlight a GBC, he soldered a wire to the power switch for ground. When i made mine, i did that also, and it worked, but i just don't understand it. Alot of the things i make from the guides on here use ground somewhere, and I use that too, but I still don't quite understand...can ground be anything that will conduct electricity?
Some people put ground on a switch but it's not really necessary. All you need is a cut off, a circuit is like a circle. It comes out of a power source, say a battery, and then goes through the device and goes back into the battery. The battery ground is has the lowest possible electrical potential, meaning that electrons with flow through atoms and arrive at the ground to fill it up. The planet earth always has the lowest possible electrical potential. Which is why if you're shocked by static electricity it goes through you into the earth.
Well technically "ground" in a circuit is a a point in the circuit which we consider to be at zero potential and measure all the circuit voltages with respect to this common reference point i.e. ground. And it doesn't necessarily have to be 0v, it can be negative or positive. But in most dc circuits it is connected to the negative post of the battery and to the chassis if it's metal :)

+ = Positive
- = Negative (or ground)

It's the other side of the battery. ;)