Congratulations on becoming a high school student! I wish you much success and hope that you will enjoy your years there. I have taught in a rural high school with 189 students and in an urban school with 3,200 students. Big difference! However, I've noticed many similarities.
Your teachers are there to help you. Nobody expects you to know all the answers or to perform perfectly. Don't be afraid to ask questions or get some help. Teachers love it when their kids ask questions; it shows that they are interested and trying to learn. Asking a question doesn't mean that you are "dumb." Every time you ask a question, you can bet there are at least 5 other students in the room who don't know either and are glad you asked.
Everybody needs a friend. If you feel lonesome or left out, look around. You are not alone. There will be other students who feel as you do. If you have an opportunity to work in teams or to work with a partner, do that. Helping others in class is a good way to make new friends. I found students in both of the schools I mentioned to be generally friendly and helpful to each other. Some were very shy, but they came around when someone else reached out to them.
Don't be absent if you can possibly avoid it. If you are in class every day, you won't get lost or get behind. You will know what's going on! Take notes in class, keep a planner or datebook to help you stay organized, follow directions, and turn in all your work on time, even if you think it isn't "perfect." If you don't understand the directions, again, ask.
Get involved in some school activities: Find a sport or a club or an activity that you will enjoy. You don't have to be the best to participate. You don't have to be a star. Just take part and have fun. You will make some new friends and feel that you are really a part of your school.
If a serious problem develops at school, go find a "grown-up" right away! Wherever you go to high school, there will be teachers, counselors, and principals who will be ready and able to help you. These are adults who love young people and who have chosen to spend their lives working with them, trying to help them succeed and make their lives better. You don't have to struggle alone with any problem you might have.
That's all I've got! I hope it is helpful to you. Again, congratulations, and don't be afraid. The fact that you wrote to eNotes shows that you are taking charge of your future. Good for you. You will do well!