I'm getting pretty darn close to doing a "Show HN" about my new macOS paint app, called Mojave Paint. I just posted a feature tour video at https://www.youtube.com/watch?v=61FJ2xzUiIU showing how to make halftoned edges, which happens to cover a lot of of the basics including layers, alpha masks, selections, foreground/background color, gradients, etc.

I would say Photoshop is awesome but expensive (if you can look past how invasive it is for your machine), Affinity is free but "meh", I'm going for the "awesome and cheap" square of the quadrant. Find it at https://skullrocksoftware.com