Answer 1

Comments have same function in every language not only in php.

Comments are generally used to specify that what the code is doing, who made this code, when it was made etc.
In other use comments are used to describe what perticular statement do.
For example I have a statement to add two things. . . .
$a = $b + $c; //This statement add two numbers.

Comments are always ignored by compilers and interpreters.