Old Linux User looking to learn.

I've use linux for about ten years. Started when I got a free ancient latitude from a school that was giving them away. It had xp and I didn't want to pay to update this project and discovered mint. I used Mint, ubuntu Mate, Manjaro, opensuse etc. I can barely scratch the surface of the capabilities. I've thought of jumping into Arch because I really want to learn to code) program. Any tips for me to start learning?