This is a great question, one in which I actually questioned my college adviser right before officially changing my major to Mathematics. The answer that she had given to me was, "Anything". Great right? Yes - as it's reassuring that so many doors are open, but no in the sense that it's slightly overwhelming not to have a direct answer of what's next.
Some obvious answers that Mathematics degrees typically enter into is Teaching, Business - Finance or Accounting roles, Actuary work, or Statistical work. The truth is, Mathematics is so much more than what people think and realize. Every class that you take is more than numbers or solutions, it's about processing what's in front of you, questioning the task, analyzing what you know and problem solving many potential different scenario's. You become detail oriented, organized, and methodical, while also trying to determine the best course of action for the situation at hand. Mathematics gives you an understanding of figuring out different ways to think and process tasks, which is incredibly beneficial to you as well as many employers.
There is a book called "101 Careers in Mathematics" I suggest you read, which my adviser in college pointed me to read as well when I declared Mathematics as my major. This will give you an idea of the endless possibilities that Mathematics opens the doors to. I would recommend thinking what interests you and what excites you when you think about your career.