@ is the supression operator. Any errors that may be tossed by the usage of the function are ignored. @ is almost never required with proper error checking and trapping.
As of PHP 5.5, the MySQL library has been officially deprecated. It is recommended to move to either MySQLi or PDO libraries for your mysql connectivity. See here for help choosing which interface you prefer: http://php.net/manual/en/mysqlinfo.api.choosing.php