What's the difference between Session and Cookie? 

The mail() function allows you to send emails directly from a script.

PHP’s configuration file is called php.ini.

There is a decent page in the php manual on the subject, in short mysql_pconnect() makes a persevering association with the database which implies a SQL join that don't close when the execution of your script closes. mysql_connect()provides just for the database new association while utilizing mysql_pconnect , the capacity would first attempt to locate a (relentless) connection that is as of now open with the same host, username and password. On the off chance that one is found, an identifier for it will be returned as opposed to opening another connection... the connection with the SQL server won't be terminated when the execution of the script ends. Rather, the link will stay open for future use.

$filename = "/home/user/guest/newfile.txt";
$file = fopen( $filename, "w" );
if( $file == false )
{
echo ( "Error in opening new file" );
exit();

}
fwrite( $file, "This is a simple test\n" );
fclose( $file );

The PHP default variable $_PHP_SELF is utilized for the PHP script name and when you click "submit" catch then same PHP script will be called.

We can send 1024 bytes utilizing GET() yet POST() can exchange extensive measure of information and POST is the protected strategy than GET technique .

These two methods are bulid-in methods  in php. with  construct() we can overwride the parent class method. The inverse of the __construct() PHP capacity while making another class, is the __destruct() technique. The __destruct() technique will consequently keep running, after you've completed with the PHP class.

Notify URL and Return URL is used in Paypal Payment Gateway integration. Notify URL is used by PayPal to post information about the transaction. Return URL is used by the browser; A url where the user needs to be redirected on completion of the payment process.