Don't worry if you do not understand a new topic right away. As you read more about it and work through the problems, you will gain understanding. Each time you look back at a topic you will understand it a little better. Not very many mathematics students understands each topic completely right from the start. Read your text carefully.
Many students read only enough to get by, usually only the examples.
Reading the complete section will help you to be more successful with the homework problems. And, YES, mathematics books are not easy to read. Do practice exercises. Rework the problems in the lecture notes before starting your practice exercises. This will reinforce the concepts presented.