It typically takes about 2½ days to complete the PADI Scuba Diver course, which has 3 parts: theory, confined water sessions, and open water dives. Theory involves watching videos and taking quizzes to test your knowledge, and this can be completed online before you arrive on the island to save more time.
During the confined water sessions, you will learn basic skills such as the functionalities of the scuba equipment, how to control your buoyancy, what to do in case a problem arises, etc. Then you progress to the open water dives, where you will be swimming underwater with the fish, applying some of the skills you learnt, and having a lot of fun.