What I did was search for a few simple Procreate youtube tutorials and mimic them. I found these ones good--even if the end product isn't something you are aiming for, you get the basics down in creating them: https://www.youtube.com/watch?v=yqRhbjUQ7Qg https://www.youtube.com/watch?v=EJQpezkDuCQ&t=876s https://www.youtube.com/watch?v=iZI-qM7PdDM
I've tried Adobe Sketch and a couple other smaller names, and Procreate is the best to me so far. It has a HUGE community behind it, so similar to a popular programming library like React, you'll be able to find a ton of online resources to help you.