If a car is Left Hand Drive, the steering wheel is on the left if sat in the cabin. Left hand drive cars are found in countries that drive on the right of the road.
Right Hand Drive cars feature the steering wheel on the right if sat in the cabin. These cars are found in countries which drive on the left of the road. UK vehicles are Right Hand Drive.
In the UK we drive Right hand drive (RHD) vehicles on the left of the road meaning our headlights are aimed slightly towards the curb. If this was in a Left-hand drive (LHD) country, the beam of light would be aiming into the other lane of traffic rather than the curb. This also affects mirror glass and mirror units. Many of the driver side mirrors in this country feature a convex curved glass to ensure the driver has increased vision, often to cover their rear blind spot. As you can image, just like headlights, this is the opposite side in countries driving on the right with LHD vehicle.
When looking at parts, RH and LH state which side of the vehicle the car fits as the image below shows!