IF as Page

Hello,
in my page I used this code to put several pages into one file.
This was very useful and would like to incorporate this in this framework as well.
But how is the URL address to call the content "edit"?

PHP Code:

<?php
    if(isset($_GET["action"]))
        {
            $action = $_GET["action"];
        }
    else
        {
            $action = "";
        }
        
    if ($action == "")
        {
?>
hallo
<?php
        }
    if ($action == "edit")
        {
?>
du da
<?php
        }
?>