Props spin either clockwise (standard or right-hand rotation) or counter-clockwise (counter or left-hand rotation).
Most single engines use a standard rotation. Most twin engines use one of each. To determine what rotation you have, look at your prop as if on a boat. Position a blade pointing straight up. If the right-hand side of the blade is closer to the hull than to you, it's a standard rotation.
A boat with twin engines and two boat props spinning in the same directionats will have a lot of steering torque. Two right-hand (or standard rotation) propellers pull the stern hard to the right and the bow to the left.
Using both standard and counter rotation with twin engines will eliminate the steering torque. This gives you better straight-Line tracking and helm control at high speeds.