A right-handed holster is designed for a right-handed shooter. A left-handed holster is designed for a left-handed shooter.
Here’s where people sometimes get confused, as it relates to one particular type of holster design (a “crossdraw” holster). If you are right-handed, your holster will generally be worn on your right hip. No confusion there. But if you are right-handed, and want to carry crossdraw, a crossdraw holster generally places the gun on your left hip. But you must still request a right-handed holster even though the holster will be designed to ride on the left side of your belt. If this describes you, just be sure to clarify that it’s a crossdraw holster you’re looking for, and that you’re right-handed, and you should be good to go.