Curves are one of the most powerful and, without a doubt, the most used tool in the arsenal of color correctors. Image processing starts with setting the color balance. Further, the contrast of the plot-significant elements of the image is increased. All this is done with curves. They are used not only for image processing, but also for finalizing masks and presets for mixing channels and blending in various modes.
This basic online master class by Andrey Zhuravlev will significantly advance you in understanding the logic of work and the use of curves, and real development will occur as a result of practical exercises.