I have only started using photoshop yesterday, so I have virtually no experience and no idea what I’m doing.
What I want to do is:
1- overlay a map of river paths on top of the desert map, and change the color and opacity of some of these rivers.
2- change the colors of the desert to green (realistic looking green land). Also, I want to preserve the original features of the land such as mountains, canyons, valleys, etc)