What is HDR? It's High Dynamic Range... meaning there is a big difference between the lights and the darks in an image.
The human eye, which sees in HDR, is able to see 19 stops. The best camera can only see 10 stops. A good example is if you take a photo from inside your living room and include a window with a bright, sunny day outside. When you expose correctly for the outside, the room inside is dark... Ambient light is often the best color so you have not added a flash to this photo.
The HDR technique- 3 photos are taken on a tripod at 3 different exposures. The software will stack these photos and when it sees dark, it will use the information from the lighter area to add to the dark areas, and visa versa. The result is a much more vibrant and better exposed photo than a single shot would render.
Below are some examples. The first photo in each set is the single shot, properly exposed photo, the second is rendered using the HDR technique. You will see there has been other editing like removing exit signs. The best way to see the HDR effect is to arrow back and forth.
Studies have shown that a high quality photo will be viewed 60% more than a low quality photo. The quality of the shot reflects the quality of the subject...