I forget why I did it now, but I taught myself to touch type when I was a teenager. In retrospect, a pretty strange thing to do, but I've felt smug about the skill so often since then that it was very much worth it.
I imagine there are lots of on-line courses, some of which may well be free, but I just used a book with exercises in which essentially start with asdf ;lkj and progress from there. It's just repetition and learned response; easy, but the structure of exercises helps a lot. IIRC, it took about an hour a day for a six week summer holiday to get to a worthwhile speed (60+ words per minute). If you don't want to invest in a 'proper course', the 'just a book' approach can certainly work.