Sessions can only be accessed after a page refresh when they are set. You'll need to reload the page to be able to access the session variables.
Another note: Everywhere you want you use any kind of session, you'll need to start the session with:
session_start();
So your get.php file would look something like this:
<?php session_start(); ?>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<link rel="stylesheet" href="style.css" media="all">
</head>
.....etc
