Not sure if this will help, it includes examples.
https://ca.ixl.com/standards/manitoba/math/grade-9
Is it possible that he is getting hung up on the descriptive wording and needs them explaining in basic language with examples. From looking at the way the syllabus is written I can see that being a problem, more so if he has missed a lesson somewhere.
I know I could never understand parts of math until by brother explained things in simpler terms.
Perhaps talk to the teacher yourself about your concerns, they will appreciate your involvement and would never belittle your own knowledge. Each of us has our problem subjects we cannot all be Einstein's.
Best wishes and your son is lucky that you care enough to want to help.