request global variable php code example

Example 1: what does $request do in php

$message = "";

if($_REQUEST['msg'] == "new"){
    $message = "New User has been added successfully";
}else if($_REQUEST['msg'] == 'edit'){
    $message = "User has been saved successfully";
}else if($_REQUEST['msg'] == 'update'){
    $message = "User(s) has been Updated successfully";
}

Example 2: how make a variable global php

$a = 1;
$b = 2;
function Sum(){
    global $a, $b; // allows access to vars outside of function
    $b = $a + $b;
} 

Sum();
echo $b; // output is 3