The first situation: I don't know anything about high school mathematics, I can't understand what the teacher is saying in class, and I can't do my homework after class. At this time, you should start from the basic questions and start from the beginning. Don't think about how fast you can improve. Start with simple steps. At this time, you must not worry. Search for some basic questions and print them out, step by step, and then be sure to be willing to ask the teacher. If you don't understand something, you must ask the teacher to answer it in time.
The second situation: high school mathematics has reached a certain height, and listening to the teacher's lecture has little effect on the promotion. At this time, you can go to the Internet to watch some difficult online classes to learn, and you can also look at the knowledge of advanced mathematics, which will also improve your mathematical thinking. At this time, you also have a clear understanding of yourself. You really can't improve much, and you don't have to be paranoid about one thing. They all need balanced development.