Krita is a good app. I have also done some digital work in GIMP and Inkscape before.

Sometimes a tablet-pen thing like a wacom can be helpful in getting smoother coloring/shading.

The best thing is to start drawing, and do it as much as possible. Even if it's not digital, keep doing it. You'll get there :)

I do pencil sketches and scan them into the computer. You can do that and then go over the lines with a digital tool, and color them in on a new layer.