A free photo editor that starts with the light: screen brightness fools your eyes, the histogram doesn't. It counts how many pixels sit at each brightness, from pure black on the left to pure white on the right. Three shapes tell you almost everything.
A photo hides what an adjustment really does. Each strip below is a grey ramp and a band of colours run through the same pixel code as the editor above, so you see exactly which tones each slider moves, and which it leaves alone.
Each step changes what the next one sees. Sharpen before you crop and you waste detail on pixels you throw away; boost colour before fixing exposure and you'll have to redo it. This order avoids going back.
These do a single edit faster than the full editor, and handle batches of photos at once.