Determining propeller rotation is by looking from the rear (AFT) of the boat forward to the front (BOW) of the boat.
The most common propeller is right hand (clockwise) rotation. The cutting or leading edge of the above propeller is on the right hand edge which is the lowest. The highest edge above is called the trailing edge. This edge may also have a rolled section which is called a Cup
Above: Counter rotation propeller rigs (both left and right hand propellers fitted)
Above: Dual right hand propeller rig
Above: Volvo Duo Props