I started with HTML and CSS because I liked to build my own useless small websites. Then I noticed it was nice to copy+paste some javascript scripts someone else wrote into them to get some "fun" interactive components. Then I slowly started to make little changes to those scripts and that way slowly learned more and more. It was not the quickest way to learn, but the most fun, because there was little setup necessary (I literally used windows notepad to save files as .html and opened them in my browser) and I could quickly see results.

Since you're interested in FOSS I assume you use an OS with a nice terminal. You could write some bash scripts to do simple tasks for you maybe? (Maybe write a script that removes old downloads from your downloads folder, or something that can delete all files that end in '.temp' (IDK just stupid ideas that could be fun to try to start coding).

Python is a nice option as well, it has a lot of useful options and documentation and gives you very readable code, making it easier to learn good practices!

Just make sure you do something fun and you will learn what's necessary along the way.