Hi Skylar! It's great you're getting started early!
First off, do some exploration on medical school and what it's really like, as well as why you want to be a doctor. So many freshmen start out as pre-med, but once they take a difficult class or have to take the MCAT, they realize that it's not for them. Skip this step and do the self-reflection NOW. If you want to help people, there are a million other ways you can do this other than be a doctor. If you are interested in healthcare, there are also a thousand other professions you can do that don't require medical school. Find out 1) what being a doctor is REALLY like by talking to a doctor or your career counselor and 2) make sure that it's the right fit for you.
Secondly, you want to be prepared by looking up the pre-med course requirements and registering for those classes at your college. Take a good look at what you'll be getting into and look over some textbooks that are for those classes. Find past syllabi for those courses to get an idea of what they'll be about. Remember that having a high GPA is critical if you want to get into medical school, so be prepared to go to office hours, get tutoring, join study groups, and do whatever it takes to maintain that high GPA.
Lastly, after you get to college, get involved in something. Whether it's a student organization, club, or job, go out and get experiences that help you grow as a person, learn about what you like/don't like, and have something to put on your resume.