I learned first by borrowing books from my local library and then from Robert J. Lang books I bought. But that was before the Internet. Nowadays YouTube is an excellent resource for learning some foundational folding principles, some base folds, and getting past tricky "folding bottlenecks" that were always a huge frustration for me when I was learning from books. It's just really hard to clearly convey some 3D folding steps with only 2D diagrams. For example some of Robert J. Lang's phenomenal insect models (https://www.amazon.ca/Origami-Insects-Robert-J-Lang/dp/04862...) are hundreds of steps, and it's super frustrating to get stuck at say step 130 with only 45 left to go.
Anyway, I prop up an iPad up with Youtube and work through models with my 6 year old son, and he's learning way way faster than I did when I was his age.