The eyes, shading, and expression are all fire! Looks stunning!
Might want to consider using different types of brushes. Looks like below 100% opacity standard round brushes. I really like the effect I got once I moved away from those brushes. Might be worth experimenting.
Thank you!
If the laptop screen has pressure sensitivity, and came with a stylus, you are golden. I use krita on desktop, with a graphic tablet. It's a Huion, i don't know the dollar price but it was cheap and it's quite decent. You may have a lot of software choices like Photoshop, Clip Studio Paint etc but I'm on Linux so Krita is the best option for me.
As for the painting process, I just rely on observation and constant failing. If you put enough wrong brushstrokes, happy accidents begin to happen eventually. Learning a little bit about values, blocking and colour theories is a good starting point.