We were all you once, and some of us still are.
You're either interested in too many things, or you can't really think of anything that you care enough about to turn into a career. You've probably seen people in your life whose careers consist of work they truly believe in that captivates them. You've also probably seen people in your life who are working jobs they find completely uninteresting and boring. You've seen people who are happy, comfortable, and interested in their careers mixed in with people in miserable careers. The only thing you know is that you definitely don't want to turn out like the latter in your future.
The fact of the matter is, you won't turn out like those people working mundane jobs and living throughly ordinary lives if you can narrow your career options down.
Start by thinking over what seems to come naturally to you. The reality is, almost no one excels at every single subject they tackle in school, but it's likely that there is at least something you're good at, or at least something that intrigues you. If the career field you're interested in is something that doesn't come to you easily, that's perfectly alright. When you devote time and effort on applying yourself to what you are trying to succeed in, the easier things will come to you. Even if you don't believe you are talented at anything, the odds are, you probably have a knack for something you don't even know about.
There are also a lot of people on the other end of that spectrum. Sometimes the problem is that you have too many ideas and interests and can't figure out how to compact them into one career. Maybe you know you're a rockstar at something, but you think you would enjoy a career in a much different line of work. I personally had a difficult time juggling the billion things I was interested in and narrowing them down, but I was able to by staying focused on what I want to get out of my future career. Whether it's money, satisfaction, or anything else pulling you towards a specific career, concentrating on what will make that career worthwhile to you is important.
I'm personally someone who has seen adults who are very excited and passionate about their jobs, and I've also seen just as many adults who despise what they do for a living. I aspire to be the kind of person who loves and cares about their job, even though I didn't always have a plan thought out for how to accomplish that. For anyone else out there who doesn't have it all figured out yet, I'm here to tell you that there is hope, and you will find something you love to do that keeps you on your toes.