What is Door Handing?
Door locks with lever handles are handed, locks with knob handles are not handed.
Most lever locks are handed because they have a high quality, "European" style mechanism that provides a firm feeling, spring supported rotation downward and a solid stop at the top of the movement. Since the levers do not rotate upward, we must assemble the levers with prior knowledge of which will be on the outside and which on the inside.
Determine the handing of your door by standing on the outside of the door. If the hinge is on the right, it's a right handed door, and you need a right handed lock. If the hinge is on the left you need a left handed lock.