Instructors are knowledgable about a topic and work to pass that knowledge off to their students. Whether you work in a gym or a school, instructors are super important to the students' success.
There are lots of possibilities for you as an instructor. You could work at a health club or a gym or you could work for a school and instruct math. There are so many different instructors out there, basically any topic you can think of probably needs an instructor.
Your hours will vary depending on what industry you decide to go with. You may find some jobs require you to work nights and weekends, like if you were to become a fitness instructor, while school instructors only work during school hours. Your schedule really depends on what you're passionate and knowledgable about and when people want to learn it.