Solving exercises is important in order to check that you can apply the theory you’ve learned, but also to check that you’ve understood what you’ve read.
In the Math Drills, you find several activities for each topic. Multiplication - The Championship is a fun and efficient way of practicing the multiplication table. If you find the exercises to be difficult, it may be wise to read the textbook or the encyclopedia once more before attempting the exercises again.
When preparing for an exam, it is a good idea to practice on previous exam problems.