Electricity is like water. It has pressure and flow. We call the pressure "volts" and the flow "amps".
When we wire a building, we need to know the pressure (volts), so we can install the proper equipment. The numbers you have listed are some standards. For example, we all know what voltage equipment to install in a house and the stores all sell the right toaster and coffee maker.
We also need to know the flow (amps) so we can install the correct size wire. Too small a wire for the required flow is like a fire truck using a garden hose - the building will burn down.
Can someone explain phases?
