If you are good at going underwater and enjoy scuba diving, you can go for some necessary certifications. However, if you want, and you are good enough to become an instructor, you can go to the PADI Divemaster training program. These are not regular training with a general PADI certificate, but it is a complete program that you will have to sit through to become eligible for tests. Once you clear the criteria, you can get the permission of a divemaster instructor. You can open your school as well, or you can join some other training centers as a teacher. However, you need to invest your time in learning and cleaning all the modules.
The divemaster course can last for many days and depends on your speed. Those who already have other certifications and are expert undersea divers can take six weeks, and for others, the classes can last for up to 6 months.