Gimp overview
More info on https://opensourcetechtrn.blogspot.com/
Download GIMP
https://www.gimp.org/downloads/
https://www.gimp.org/docs/
https://www.gimp.org/tutorials/
iPhone image source: https://techupdatess.com/its-time-to-...
(again not mine, just used for the tutorial)
Ton more other info is available, confirmed GIMP is roughly 25 years old, so a lot of info is out there if you Google.