When the lesson includes something you don't understand, ask about it right away. Get some after-school help within a day or two. Back in grade one or two, you had to master reading and numbers, or you didn't pass. That was because those skills were essential for everything else that followed. In math, this will mean you will probably not pass that next course.
Nothing can substitute for a full period of class time, asking questions, and practicing problems.
More than one or two days' absence per month are too many , if you want a good mark. All the Homework Believe it or not, there actually is a reason for homework. Most of your learning happens when you attempt to answer some questions, not while you are listening to the teacher. Doing most of the homework, or doing it most of the time, is not good enough. Notice also the word 'attempt'.