This is from a long time ago, many years ago. I didn’t have my iPad Air then, just some PC programs and my graphics tablet. As usual, I was just winging it, trying to come up with something. The program I used was MyPaint, a simple yet excellent digital painting program. I encourage you to try it out. You may become addicted!
Note: I have to look to see if Mypaint is still available. If not, there are other similar options, which I may discuss here.