What does the main relay do? I seem to have a problem with the fuel pump and/or main relay. Sometimes there is no sound when I turn the key.

Does the main relay have any other purpose beside operating the gas pump?
If there is something wrong with the main relay, will the car stall after the car has started and is running? My car sometimes vibrates and feels like it is going to stall, unless I step on the gas pedal.

Thanks