Given that 1) you have zero problem grasping the concepts and understanding the examples, and 2) your difficulty is in solving the end-of-chapter problems; I th

Given that 1) you have zero problem grasping the concepts and understanding the examples, and 2) your difficulty is in solving the end-of-chapter problems; I think it is almost certain that your issue is one of making small mistakes that throw off your solutions (for example, didn't change a plus to a minus sign, left off a term, made an incorrect assumption, etc.). You just need to learn how to double-check your work and figure out where you went wrong. This is a skill that everyone doing nontrivial math has to learn. In a formal learning environment, you constantly get feedback on your mistakes through the grading process, which you obviously don't get when self-learning. My advice is to work the example problems before looking at the solution. After you have worked it yourself, you can then easily see where you went wrong. You should also get books of solved problems that let you practice this more extensively. There are problem books for pretty much every undergrad math topic as well as some grad-level ones. A lot of textbooks even have solution manuals that will show you how to solve the end-of-chapter problems in the textbook. An Amazon search with the word "solutions" and whatever math topic you want should turn up many examples. With practice, you learn how to detect errors and rectify them even when there is no solution manual.