There are thousands of different kinds of jobs that one could do as a marine biologist. The jobs could be indoors or outdoors, usually some of both, and of course could take place anywhere in the world where there is an ocean. At least 150 countries and island states have marine coastlines.
Many marine biologists do several of the above during their career, as well as many other things.
The amount of schooling you need depends upon what you eventually want to do in the above list but a university course which includes marine biology courses will start you out on the right track. However, a broad education is extremely useful and it should include a wide range of courses at every level. Not all marine biologists have PhDs but many find it useful for obtaining certain jobs. Probably the most important thing is enthusiasm, raw drive, and dedication. In my own career, I started in the early 1970s as a film maker and my introduction to marine biology was being asked to film orcas in the wild as part of a film crew.