HDR (High-Dynamic Range) is a photo processing program. When shooting in a big light environment, the ordinary camera can not record extreme bright or dark details due to the dynamic range. Even if the image is processed by HDR program, even in the case of big light ratio, both high and dark positions can get a better level than ordinary photographs.
That is, the high dynamic range, when the object's brightest and darkest part is very different. After the HDR is opened, three photos will be taken, which correspond to under exposure, normal exposure, and overexposure, and then combine the three pictures into one piece and highlight the best parts of each picture to create a wonderful picture.
That's why when you open the HDR mode, your cell phone takes longer to take photos. In fact, it took three pictures, not one. The advantage is that the image is not seen through the camera, but more directly seen by the human eye. In short, HDR can make the bright, darker, brighter and darker details more plentiful.