It's difficult to deal with ADHD without outside help. The key for you is to find systems that work for you, and to ask adults or friends to help you with those systems.
Tips to help you in school and doing homework
Sit near the teacher in class.
Turn your phone off or put it away.
Talk to your teacher. Teachers appreciate honesty about your challenges and don't want you to struggle.
Exercise regularly and move around when you can. It helps with focus.
Take regularly scheduled breaks. Ask the teacher if you need them more often.
Learn to meditate. There are plenty of apps that can helps with that.
Celebrate the things about you that are awesome. ADHD does not define you.
Here are five statements/questions you can say to adults to get help managing your challenges.
"I need help remembering..."
Do you forget to take your homework to school? Forget to take your medication? This sentence can get an adult to help you get a system to remember something you often forget.
"Can you help me figure something out?
Sometimes the way your brain works differently makes a situation not make sense. Instead of getting mad (and it's really easy to get mad), ask why.
"Can you help me explain that I'm trying my best?"
Sometimes adults say "Just try harder" about things like remembering, organization, or moving around. You can ask another adult to help you explain how hard your challenges are for you.
"Can I get a copy of the teacher's notes?"
This is something I wish I had done for myself in high school. The teacher made us copy his notes exactly, but if I didn't listen to his explanation, I didn't understand what was going on. I was miserable and embarrassed that whole year, while I could have just asked the teacher for the notes to copy later.
"Can I work somewhere quieter?"
If the classroom noise is bothering you, you can always ask to go somewhere else. Your helper teacher might be able to help or your school counselor. You don't have to sit there and suffer.
References
Hasan, S. (Ed.). (2022, May). ADHD: Tips to try (for teens). KidsHealth. Retrieved June 22, 2022, from https://kidshealth.org/en/teens/adhd-tips.html
Morin, A. (n.d.). Self-advocacy sentence starters for middle-schoolers with ADHD. Understood. Retrieved June 22, 2022, from https://www.understood.org/en/articles/5-things-your-middle-schooler-with-adhd-can-say-to-self-advocate