Hehe, I am a self-taught college mathematics student. This is a good way to read textbooks. I can look up many related books in the library by myself. Suggest looking for something simple. Here is a trick, you can choose a thicker book, because such books are often very detailed and fulfilling. Be sure to take study notes and understand the examples. Take your time. If you concentrate on your study for a month, you will certainly learn well. I taught myself indefinite integral for two days, and then it was difficult, but just stick to it. I wish you a happy study.