The Fitness industry is a huge industry -- encompassing every type of employment position you can think of.
It all depends on your experience, your education, your desire, your work ethic and your goals. It could be business-oriented like gym owner, or training oriented like personal trainer, or work oriented like fitness equipment mechanic, or specialized like fitness photography.
It's not a quick answer we can just throw at you. It's something you gotta give some time and though to. Some research wouldn't hurt either.