All of the above and none of the above. Some of the finest photographers ever, have never done any formal training. Others have done more training than probably a dozen AP members combined.

It really is up to you, and each person learns differently. Some learn from books, others learn better watching video instructions (youtube etc). Yet again other learn by hands on watching and then doing, with a mentor. You need to understand yourself and what modalities of learning your brain is best suited to, then go with that. There is no 'one approach suits all'.

Work out how you learn, then embrace a learning plan using that structure, devices, etc.