i cant understand this code in php

    <div class="wrapper">

        <h1>Contact</h1>

        <?php // if status=thanks in the query string, display an thank you message instead of the form ?>
        <?php if (isset($_GET["status"]) AND $_GET["status"] == "thanks") { ?>
            <p>Thanks for the email! I&rsquo;ll be in touch shortly!</p>
        <?php } else { ?>

            <?php
                if (!isset($error_message)) {
                    echo '<p>I&rsquo;d love to hear from you! Complete the form to send me an email.</p>';
                } else {
                    echo '<p class="message">' . $error_message . '</p>';
                }
            ?>

            <form method="post" action="<?php echo BASE_URL; ?>contact/">

                <table>
                    <tr>
                        <th>
                            <label for="name">Name</label>
                        </th>
                        <td>
                            <input type="text" name="name" id="name" value="<?php if (isset($name)) { echo htmlspecialchars($name); } ?>">
                        </td>
                    </tr>
                    <tr>
                        <th>
                            <label for="email">Email</label>
                        </th>
                        <td>
                            <input type="text" name="email" id="email" value="<?php if(isset($email)) { echo htmlspecialchars($email); } ?>">
                        </td>
                    </tr>
                    <tr>
                        <th>
                            <label for="message">Message</label>
                        </th>
                        <td>
                            <textarea name="message" id="message"><?php if (isset($message)) { echo htmlspecialchars($message); } ?></textarea>
                        </td>
                    </tr> 
                    <tr style="display: none;">
                        <?php // the field named address is used as a spam honeypot ?>
                        <?php // it is hidden from users, and it must be left blank ?>
                        <th>
                            <label for="address">Address</label>
                        </th>
                        <td>
                            <input type="text" name="address" id="address">
                            <p>Humans (and frogs): please leave this field blank.</p>
                        </td>
                    </tr>                   
                </table>
                <input type="submit" value="Send">

            </form>

        <?php } ?>

    </div>

</div>