Ho un ile che si chiama register.php.
Sul quale c'è questo form:

Codice PHP:
 <html><head>     <title>Registration Module</title>     <link href="css/access.css" rel="stylesheet" type="text/css" /></head><body>     <form id="login" action="register.php?do=verify" method="post">        <fieldset id="inputs">            <input id="username" name="username" type="text" placeholder="Username" autofocus required>            <input id="password" name="password" type="password" placeholder="Password" autofocus required>            <input id="email" name="email" type="email" placeholder="Email" autofocus required>        </fieldset>        <fieldset id="actions">            <input type="submit" id="submit" name="action" value="Submit New Registration">            <a href="login.php" id="back">Have already an account?</a>            <a href="index.php" id="back">Return Back</a>        </fieldset>    </form> </body></html> 

Come faccio a fare un codice php che agisca quando siamo su register.php?do=verify ?
Vi prego rispondete!