What courses can I take in college/high school to become a graphic designer?

If your school offers digital art take that and any art classes offered will help to gain skills.

I'd suggest trying out a few different types of digital design, because there are lots of different potential careers that could be a good fit for you to combine a love of art and technology. A graphic design class could give you experience with learning text & graphic layout. I took an animation class in college where I learned how design could be used for storytelling and in an interactive web context. Learning more about digital photography and editing can also be helpful when working on projects or a portfolio. Lastly, learning at least a little bit of web design (maybe some HTML and CSS) can open up a whole different side of career opportunities if you find it's interesting to you.