Don't worry, everyone has something they don't understand. There is nothing to be ashamed of. You can only learn if you don't understand. You should think, if I know everything, do I still need these classes? You don't have to come. But it's good to be with good classmates if you can bear the relative pressure. You can ask others what they think. Don't worry, just because you don't understand now doesn't mean you won't understand in the future. And they just understood it before you. Believe in yourself! If you feel embarrassed, you can ask the teacher privately. I'm sure the teacher won't laugh at you. After all, you have the heart to learn. Come on! Nothing is certain, you can do it.