Well level of mathematics in AFCAT is not difficult. But there are some calculative questions are asked but you can eliminate them by approximation.

Considering if you are beginner and starts from zero then you should start preparing each topic one by one from youtube. You don't need to bother about whether teacher is of defence background or not you just need to complete each topic. One important thing is you don't need to prepare for advance math basic arithmetic is more than enough. Complete the syllabus as early as possible and start practicing for that .

All The Best.