Do you want to press button A to make the motor revolve clockwise and when the button is released, the motor stops.
Wait a second (you must wait a second) and press button B to reverse the motor and when the buttonn is released, the motor stops.
To do this, you will need to wire two of the relays.
The output of each relay has 3 pins or terminals. One is called NO for Normally Open, the other is NC for Normally Closed and the other is Com for Common.
The common pin or output or terminal touches the NC pin when the relay is not energised and clicks over to the NO pin when the relay is energised.
Find the Com pin of relay A and connect it to the motor. Find the Com pin of relay B and connect it to the other side of the motor.
Now connect the NO terminal of each relay to the 12v supply and the NC terminal of each relay to 0v.
Done.