Thanks for your great question about pursuing band in high school / college. I'm so glad to hear that you want to play in college! I played in my high school band and currently play in college as well. If you're looking for a space to continue playing your instrument in a group setting, I would recommend asking around to see if there are any active community bands in your area. Many people like you want to continue playing their instrument, and often times that leads to concert and jazz bands being formed.
If you're looking for a more committed experience, you could look into a drum corps. These are on an audition basis (colorguard, drumline, trumpets, horns, etc.) , and many drum corps travel around the country to compete. Here is a video of my favorite performance: https://www.youtube.com/watch?v=qOMjdUhkH5E
If you're looking for more theory-based resources, you could pursue AP Music Theory: https://apstudents.collegeboard.org/courses/ap-music-theory! With a quick Google search you'll find many books, videos, and other resources to help you pursue music theory.
Neel recommends the following next steps:
- Check to see if there are any community bands in your area
- Check to see if there are any drum corps with openings in your area
- Look into AP Music Theory to see if that's something you're interested in