Answer 1

There are more than one reason we use comments
1- to remind what we have done in the programme for later developing
2-to let other developers to understand the codes
3-if you want your code will be accepted by the community it is kinda a must
4-some compilers use those comments to create documentation of the programme so even while running programme you can understand how it works - I am not saying exact mean of manual but sort of it.

I am pretty sure some of our frineds will add some more benefits of comments

multi comments is just trying to help reading cause comments are not responsive