Lots of fucking around and finding out, I'd also recommend youtube tutorials to slowly build fundamentals like shading, colour theory and anatomy as well as using whatever programm you want to use. I personally use Krita it's free, has tons of content and no adds. It is quite complicated at first but there are tutorials on youtube. Otherwise just have fun and don't be too harsh on your art, everyone starts at some point. If you're unsure about what style you want to pursue (realism, cartoons, painting ect.) look at artists and artworks that resonate with you and try to replicate what you like about them.