I would suggest starting off with Art Rage by Ambient Design.
I would suggest starting off with Art Rage by Ambient Design.   This program will run on Macs, Windows and even Linux using the WINE application on Fedora or Mint operating system variants of Linux.    Art Rage is a very good program for digital painting and drawing.   Cost is reasonable under $100 with upgrades of new versions in the past have been 50% of regular cost.   This program has: oil brushes, watercolors, air brushes, paint rollers, pencils, paint tubes, glitter tubes, ink pens, gloop pens, palette knives, pastels, sticker spray, and custom brushes.   Program includes complete editing features.