How to obtain the session in php

In php, how does one get the session in the shopping cart? what does the session mean? How does one get the session value? How does one write the shopping cart program, thank you ------ solution ------------------ first session_start (); then you can directly set the session $ _ SESSION [val] value; then you can get the session in php on other pages.
In the shopping cart, what does the session mean, how to get the session value, and how to write the shopping cart program? who knows? send me one. thank you!

------ Solution --------------------
First session_start ();
Then you can directly set the session.
$ _ SESSION ['Val'] = 'value ';
You can directly use this session on other pages after setting
Go to the internet and look for "PHP and MySQL Web Development". the source code of the shopping cart is made by session.
------ Solution --------------------

Session_start ();
Session_register ("G_loginuser"); // login id, which can be used to authorize a user

Get $ G_loginuser = '$ ';