I took this photo in Peru, NY of Lake Champlain. This is a 30 second exposure of the sunrise I woke up for at 6:00AM. The top photo (before) is the RAW file directly from my camera while the bottom one (after) was edited using camera RAW. Camera RAW is a very useful editing tool used to correct the exposure along with all other types of settings. If you did not shoot the photo in camera RAW and still wanted to edit the JPG or PNG like a RAW file, it's simple! All you have to do is convert your photo to a Smart Object (right click on the layer > Convert to Smart Object) or go through the menu bar (Layer >Smart Objects > Convert to Smart Object)***. After converting to a Smart Object, now go to Filter > Camera Raw Filter. After clicking this, a window will pop up with all these different settings and tabs. From here, you can change the exposure, highlights, vibrance, etc. On the other tabs, you can chose to change the curves, sharpen the image, lens correction, as well as many other useful settings. At the top of the Camera RAW window on the right is a "Color Mountain" this is the Histogram. The histogram is a tool used to properly expose and color your image. If the histogram is skewed to the right, then it is underexposed. If it is skewed to the left, then it is overexposed. The camera RAW filter is a good tool to use to correct the skewing (proper photo exposure). In the top left, there are a few tools which include spot removal, radial filter, and graduated filter.
***This step is not necessary, but it is more convenient to see the before and after image as well as edit the changes you have made.