Treat each signal as a water pipe. At the microphone (or instrument) the signal (water) enters the “pipe.” It has to travel from there to to the mixer, through the mixer, out to an amplifier (or through a built in amplifier) and to the speakers.

Individual signals come in, go through EQ, and individual volume controls. The result is controlled by the master volume section and then the final signal heads for the amps. Get the manual for your specific board because each board is slightly different on the fine details. 
A good overview is Soundcraft Guide to Mixing (Youtube).

Monitors – Aux sends

Aux sends are volume controls that tap off a signal to send it to a different output than the mains. These are usually used for monitor signals or group effects such as reverb.

Note that AUX channels can either be before the fader or after the fader. Usually sending a signal to the monitors will be done on a Pre-Fader AUX so that the volume heard on stage is the same regardless of your mix in the house.