my dream job found me.
as for career, well i always knew what i wanted to do. i wanted to become an accountant (profession) and also writer (which was more of a hobby). i knew i wanted thse two even from junior high school. and so i took courses for both in high school, then studied writing a bit online while also writing a lot, reading books on the craft of writing, and of course reading. and for accounting, i went to college and intitutes for accounting study, accounting software, etc., where i also took courses that would help my writing whenever i could, such as course on doing research, etc.
The best place to plan your career is of course in high school so you don't waste time later. but it's never too late to plan. there are career planning courses and you may be able to find something online as well to help you reach a decision. think about the things you like to do and the subjects you're interested. your career should be something you enjoy because you'll be doing it for many years. switching to other careers later on are time consuming and costly so plan well and choose what you love doing while also think whether you you can do that sort of work of not. For example, i loved both library arts and accounting but chose accounting (probably loved it more) but it's not always easy getting a job in this profession because a lot of companies deal with interest so i sometimes wonder if becoming a librarian might've been better for me, especially since i love reading and writing.