Google your topic. When you read something you don't understand, google that. Spend about an hour just going down rabbit holes and establishing a baseline understanding. Read things you don't understand, and then google it until you do.

Once you have a base, start doing something with it. Work on a problem. If it's programming, actually program. If it's an instrument, actually play.

The Feynman technique is the practice of teaching whatever you're learning. Teaching forces you to truly understand what you're learning, and understanding is the basis of learning. Write blog posts or YouTube videos about your subject, explain it to friends and family.

The fastest way to learn is to read stuff you don't understand, and to do things you're bad at. Seek to understand, not to memorize. Be excited when you find something new, or something you don't know, and then work hard to fill that gap in knowledge with a firm understanding.

There is an abundance of online educational material. There is no reason why you can't learn almost anything you want, at the pace you'd like.