How relay operate?

Same as every other relay. All relays have a control side and a load side. The control side has 1 power and 1 ground. It also has a coil of wire that becomes electromagnticly energized causing the LOAD side to close and allow current to flow. So you hop in, turn your ignition key and then the request is sent to the ECM (cars computer) to see if the conditions are correct for the car to be started. The control side of the relay is then energized by the ECM providing a ground for the relay. Current will then be allowed to flow as the control side causes the load side engage.