Hey there! =) I'm more than happy to help out, so feel free to ask any questions that come to mind, whether it's today or further down the road.
I decided that I wanted to pursue a career in therapy during my junior year of high school - what a cool coincidence! First things first, see if you can obtain a volunteer role that will allow you to gain experiencing mentoring other people, providing support to them in some way, etc. For example, high school students can occasionally work within their own counseling department as peer mentors, or they can volunteer with non-profits and care for at-risk individuals, such as the homeless, recovering addicts, domestic violence/abuse survivors, etc. Your volunteer experience can be included in college applications and resumes!
Second, you'll want to start thinking about what career path you want to take. I have a master's degree in clinical psychology; however, I'm not a clinical psychologist. In order to become a psychologist, you'll need to get a doctorate degree. In order to become a psychiatrist, you'll need to go to medical school. If you want to become a therapist, mental health counselor, social worker, etc. then it could be a master's degree or bachelor's degree, depending on what kind of job you want to obtain. Learning about all the different career paths can take some time, so it's best to get started now!
Finally, once you have an idea of what career path you want to take, you'll want to start researching how to get there. For example, I am a marriage and family therapist registered intern in California. In order to become a marriage and family therapist registered intern in California, you need to earn a master's degree AND accumulate 3000 hours of experience at clinical settings. 3000 hours is a LOT of experience, so even after graduating, an intern can expect to work for 2+ years. Not all interns are able to obtain paid employment right away, so that presents another challenge. Then, after obtaining 3000 hours, interns have to pass two licensing exams. The cost of becoming a licensed marriage and family therapist can be considerable, and the salary may not be very high, so it's not a career path everyone wants to pursue; however, there can be some great benefits as well (like knowing you're making a positive impact in your clients' lives). Again, exploring all these different factors can take a while, so this is the perfect time to start researching career paths online, talk to people who have these careers, etc.!