i'm not sure what you mean exactly, but if you mean the best place to physically find extracurriculars, it's usually through your school? or you can ask people in your community about volunteer opportunities or organizations that need help, that kind of thing.
I also don't know what you mean by that, so I'll answer your question in two parts.
1: Well, I would suggest finding things that you love. For instance, if you love the trombone, join the band at you school. If you love to draw, join an art club or an art community. Extracurricular activities should showcase your talents, passion, and time management skills.
2: Like the previous answer, your school would be the best place to start. You can also search for classes and other programs in your city/area online.
To keep this community safe and supportive:
What do you like to do? Or what do you hope to major in in college? If you give a bit more information you might be able to get more specific answers for your situation