Just as in other subjects, you must know the theory to master mathematics. Get used to reading the textbook to find answers for your questions. Become familiar with its index, resources and glossary. This way, you can navigate more quickly when there are questions or topics you must examine.
Not all math books contain enough theory to explain methods, procedures and connections related to the exercises. It may be wise to use multiple sources to enhance your comprehension of the subject, for instance the encyclopedia in this portal.