How do i know when to add comments when coding?

Answer 1

By understanding the code
And make it into your heart

Answer 2

It's not required but a good and useful practice.. think of it as a documentation of the code..
So you could first start writing the structure of your code as comments and then write the code between the comments..
(Descriptions of variables, functions, sections)
Anything you learned during programming could make a useful comments like (what's a predefined function do)..
Corrections/improvements/modifications to remind yourself or others why you did what you did..
Anyway take as a way to communicate with your future self or others about that code..

Answer 3

It's your code make it a comment complete from beginning to end
nothing should be output