I learned to dive in the 1960s from a book called, I think, The New Science of Skin and Scuba Diving. I was very careful and read everything I could get my hands on. I bought my equipment at a local department store. By the early 70s shops began requiring a C card to fill your tank, so I enrolled in a course that ran for weeks. It was easy for me, but I enjoyed it and learned much that was useful despite all the experience I had by that time, especially about the technical aspects of my equipment. I'd say that certification is definitely a good idea. It's easy to get hurt in shallow water and having an experienced person walk you through it has got to be invaluable.