But... what is this "right thrust?"

You will notice on many/most planes that when looking down from the top, the motor/engine will be pointed slightly to the right. That's right thrust. The motor's not crooked or mounted incorrectly.

Right thrust helps to counteract the torque and gyroscopic effects of the spinning propeller, which is trying to make the plane go left. How much right thrust is enough right thrust? It depends on the plane, and sometimes requires experimentation.

That little diagram means to mount the motor pointing slightly to the right.