<form method="POST" action="page_next.php">
<input name="first" value="">
<input type="submit" value="Next">
</form>

<form method="POST" action="page_last.php">
<input name="second" value="">
<input type="submit" value="Next">
<input type="hidden" name="<?php echo $_POST['first']; ?>"
</form>

<form method="POST" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
<input name="last" value="">
<input type="submit" value="Next">
<input type="hidden" value="<?php echo $_POST['first']; ?>" name="first">
<input type="hidden" value="<?php echo $_POST['second']; ?>" name="second">
<input type="hidden" value="TRUE" name="submitted">
</form>

<?php
if ($_POST['submitted'] == true) {
    // your code for insert to database
    // example:
    $servername = "localhost";
    $username = "username";
    $password = "password";
    $dbname = "myDB";

    $first = $_POST['first'];
    $second = $_POST['second'];
    $last = $_POST['last'];

    // Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);
    // Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }

    $sql = "INSERT INTO MyTable (first, second, last)
    VALUES ('$first', '$second', '$last')";

    if ($conn->query($sql) === true) {
        echo "New record created successfully";
    } else {
        echo "Error: " . $sql . "<br>" . $conn->error;
    }
    $conn->close();
}
?>