The difference between the get and post submissions in a hyper-global variable form commonly used in PHP what is the difference between a session and a cookie? What does the GD library do?

hyper-global variables commonly used in PHP

$_get----->get Transfer Mode
$_post----->post Transfer Mode
$_request-----> can receive values for get and post two ways
$GLOBALS-----> All the variables are in there.
$_files-----> Upload files using
$_server-----> System Environment variables
$_session-----> Session control will be used.
$_cookie-----> Session control will be used.

differences in how get and post submissions are in a form

Get is the URL where the parameter data queue is added to the Action property of the submission form, and the value corresponds to the field one by one in the form, which can be seen from the URL, the amount of data sent by the get is small; get security is very low;

Post is through the HttpPost mechanism, the form of the various fields and their contents in the head of the HTML to prevent the transfer to the URL address referred to by the Action property, the user does not see the process, the post transmits a large amount of data, post security is high;

the difference between a session and a cookie

Session: Stores the globally unique variables accessed by the user, stored in the location of PHP (Session_dir) in the specified directory on the server;
Cookie: Used to store continuous access to a page, is stored on the client, and is stored in the user win's temp directory for cookies.

What is the GD library for?

The GD library provides a range of APIs for working with images, using the GD library to process images, or to create images.
The GD library on the site is often used to generate thumbnails or to add watermarks to images or generate reports on site data.

The difference between the get and post submissions in a hyper-global variable form commonly used in PHP what is the difference between a session and a cookie? What does the GD library do?