When I started learning digital art, I was already in college, I don't even know what is photoshop that time but
luckily, my professor is a very patient and understanding person.
My professor have to teach me one on one for the basics of programs, and I have to stay at school for longer because I don't have my own pen tab (the school provide it for student use but you can't take it home)
Then I have a nice set of blockmates and seniors to teach me and give me tips from time to time.
Then finally, when I had my own pen tablet in my last year of college, I taught myself by watching some videos on youtube and learning from digital art related books in our library. I can say that I applied my traditional drawing skills in doing digital by being familiar on textures, shadows, colors, lighting stuffs like that then try to interpret it to digital in my own way by playing around with brushes.
After learning several programs I learned that each programs have their own unique set of tools and for what type of digital are they good for (at least from what I observe) like for example:
Autodesk sketchbook - has copic brushes with the actual color codes of copic markers -- which will be easier if you want to turn that art piece into traditional, and want to color it using actual copic markers.
it can also be installed on tablets.
Paint tool sai has stabilizers -- you can use it to control the brush movement so it wouldn't be shaky, and the colors are exact when you save it as JPEG and stuffs.
Photoshop has a variety of blending tool like mixer brush -- which you can use for mixing and blending. You can customize brushes there too and it comes with post editing tools.
Medibang - they have screentones and free resources for manga and comic making, you can also download a lot of brushes. -- and its a free program
Corel painter has gel brush --- good for layering colors and doing semi realistic art since blending and the brushes' texture there are made to be as accurate as possible --- that is if you have the patience to learn each brushes' effect. also its the free program for wacom intuos art
CSP- is pretty much everything, they have nice brushes, you can also customize brushes, they have screen tones brushes, and doing lineart there is really good since it's the result is really clean. and like photoshop they have enhancement tools for post editing your work. I think its the free program for wacom intuos comic but I'm not sure what version it is.