what is strstr function does?

Ans: the strstr function is extract the datat which you want to search in the target string along with the rest data, if it will find.

exm: $tt= 'jafarkhanphp@gmail.com';
$domain = strstr($tt, '@');
echo $domain; // prints @gmail.com

Q: Why use at the Rate before any function name in php?

Ans: Some time the function generate error in the screen so to stop this type error you must @ sign before calling function.

Example :@mkdir($config['cache'], 0777, true);