<?php

session_start();
$page = 0;
$last_page = 0;

if(isset($_GET['page'])) $page = intval($_GET['page']);
if(isset($_SESSION['last_page'])) $last_page = $_SESSION['last_page'];

$_SESSION['last_page'] = $page;

if($page == 0) {
    // Prima data aici, e ok...
}
elseif($page == 1) {
    if($last_page != 0){
        echo 'Gresit! <a href="test.php">La inceput</a>';
        die();
    }
}
elseif($page == 2) {
    if($last_page != 1){
        echo 'Gresit! <a href="test.php">La inceput</a>';
        die();
    }
}
elseif($page == 3) {
    if($last_page != 2){
        echo 'Gresit! <a href="test.php">La inceput</a>';
        die();
    }
    else {
        echo 'Bravo! Perfect! <a href="test.php">La inceput</a>';
        die();
    }
}

?>

<a href="test.php?page=1">Buton1</a><br>
<a href="test.php?page=2">Buton2</a><br>
<a href="test.php?page=3">Buton3</a><br>