Start with something that you are very passionate about. Is it math, science, history, art, engineering, or something else?
Ask yourself, can you make a living doing this as a career? If so pursue it. If you do not think so, dont let that discourage you. You can find a way to do something you love even if it's not how you envisioned it.
I always wanted to be a teacher. I love helping people grow and learn new things. Currently I am a supervisor in customer service with a company I love, and I teach peopld every day. It's not how I envisioned it, but I am still doing what I love.
So use your passion to find a direction and then look for ways to make that a viable career.
What do you like to do in your spare time? What motivates you? What are you passionate about? If you had a day where you could do anything you want, how would you choose to spend it? The answers to these questions wont necessarily lead you into a career because you need to sort out what are hobbies versus what are career paths, but if you know you love spending time with animals or kids or you love building things or have a passion for understanding how things work or you love being outdoors, etc. are all indicators of the types of fields you might enjoy. Learn about yourself and what you like. Make a list and see what things could possibly have a job connected with it. What do you absolutely NOT like doing? That is important to know as well. For example, If you hate traveling, you should not choose to be a airline pilot or a salesman.
Are you volunteering anywhere? Maybe try spending some time volunteering locally with something that sounds interesting to you. If you like it, then you can explore more career options. Now is also a really good time to start thinking about a summer internship or a summer college program camp for high school students. The applications for many summer programs are due in March/April. Talk to your School Counselor about possibilities. Pick three different fields that you have even a small interest in and see if you can go spend a day shadowing someone in one of those fields.
Have you done any career inventories? Does your school offer the ASVAB? Sign up and take it! This is a free program that assesses your skills and abilities and matches you with jobs in that field. Have you taken an Meyers-Briggs test? This is a personality test which helps you understand how you relate to the world around you. There are some free online ones but I particularly like the version at https://www.16personalities.com/.
Lastly, its ok to head to college undeclared major. Spend the first year taking your core classes but exploring all the possibilities the college offers. Take an elective in a few things that sound interesting and then talk to your professors about careers in that field. Ask your academic advisor for help selecting classes that will give you a wide range of experiences so you can figure out what is the best fit!
I'm so excited that your working on planning your career. One thing I would recommend doing is shadowing your friends and relatives or possibly interview random people about there careers. It will cause for you to communicate and be proactive in building your future. I started by interviewing my parents friends as I came across them at functions or just visiting. It'll spark alot of conversation and possibly open the door to your future! Be Encouraged! Reach For The Stars! 😁