[SERIOUS] How do you do figure out what job you want after high school?

My advice is just pick a broad direction and try to optimize for not limiting your options.

When I was 18 I liked math and science so I went to school for engineering. Did I want to be an engineer? I had no idea at the time. But I figured the first couple years were mostly math and science courses anyway so if something else caught my attention (computer science, chemistry, etc) I could narrow my focus when the time came.

If you don't plan to go to college, that's cool too. My advice in that case would still be not to limit yourself. Pick something in your broad interest area that challenges you and has a clear path of advancement (certifications, etc). If you don't like it after a few years find something else. Just make sure with whatever you pick the growth path is pretty clear and at least somewhat in your control.

There's a lot of advice here to work for money and that it's a fool's errand to "follow your dreams". This is the same advice I got twenty years ago when I was 18. I followed it. That path led to money but I'm not sure it precisely led to a life of fulfillment or contentment. I often wish I'd spent more of my early twenties taking more risks and chasing more dreams. You're only young once, and age accumulates life baggage (e.g., bills , mortgage , life partner, maybe kids) that discourages risk taking. Don't forget to take a risk every now and then, you might end up surprising yourself.