It's true, every successful person begins their success with just a dream or a vision. What makes your success is your passion to see your dream become a reality and that's why it's so important to find things you are interested in.
Not very many people know what they want to do after post-secondary. High school is the time to explore your ideas. Taking a variety of courses allows you to filter out what you do and don't like.
Once you find something that interests you, continue exploring in that direction. Take a couple of more courses that give you better insight into that area. It doesn't matter if you go in one direction and find that it isn't of interest any longer because you have 4 or 5 years to explore! On the other hand, if you find courses that you do like then half the battle has been won.
Another big influence toward your goal is the ability to get along with others. Teamwork is vital. People want to work alongside others that will lend a hand or contribute diverse perspectives. Get involved in a club or team sport, they want you and you'll gain so much while having fun.
You're usually similar to what you hang around with. Peer pressure is real.
Choose your friendships carefully and go get your dream, the world needs you!