Скачать или смотреть How comparator works inside sort() method in c++.

Here one thing that I said should be other way around according to the current implementation of comparator in c++.

If you want to sort an array A=[3,2,1] in ascending order. Sort() will send (2,3) instead of (3,2) (That I had assumed in the video) in the comparator. The definition of cmp() will be like
return a less than b.
Hence, cmp(2,3) will return true so here the swapping will take place to bring 2 before 3 to make the array A in ascending order.

Remember if it return true then sawpping will happen otherwise not.

It is just the convention they have chosen while implementing in c++ although you can write your own comparotor and choose either of the two convention and implement it.