Comment is the part of code that is ignored .In html the comment is start with special character "<!-- comment here > " and it is the same here in php. There are single line comments or multi-line comments .
example of one line comment
<?php echo " Codemiles forums "; // comment here #comment here
As you saw above "//" and "#"
example of multi-line comment
<?php echo " Codemiles forums are cool"; /* bla bla bla bla All these lines are for comment