$_Post Function:

The built-in $_POST function is used to collect values from a form sent with method="post". Information sent from a form with the POST method is invisible to others and has limits up to 8mb amount of information to send.

Syntax:  $_Post[‘Variable_Name’]

$_Get Function:

The built-in $_GET function is used to collect values from a form sent with method="get". Information sent from a form with the GET method is visible to everyone (it will be displayed in URL) and has limits amount of information to send.

Syntax: $_Get[‘Variable_Name’]

$_Request Function:

In PHP, There is a built function ‘$_Request’, which is used for collect the information from form either it is used ‘GET’ method for submitting form or ‘POST’ method.  

Syntax:  $_Request[‘Variable_Name’]