Oh my gooosh how to make digital art... your best bet, aside from taking an actual class, is to find some tutorials for whatever program you're interested in! I've bumbled into several video lessons on Youtube and other places for Photoshop, for instance.
But idk man. Making digital art is like making non-digital art... same processes of drawing or painting or whatever are involved. Being able to easily undo something is a nice thing about digital stuff, but programs or a tablet can be expensive!
I drew this picture with pencil and pens and then scanned it and colored it in Photoshop... honestly, I may draw or color things in Photoshop because I'm too much of a lazy bum to dig out my real paints, not because I have any serious preference for Photoshop! :3
But yeah, babbling aside... try looking up some video tutorials... they can be very helpful!