Pentru a afisa adresa de email, am adaugat coloana `email` la query:
SELECT id, username, email, register_code FROM users;
Iar in tabel:
<th>Email</th>
Respectiv:
<td><?=$user['email']?></td>
Am adaugat in tabel:
<th>Actions</th>
<td><a href="delete.php?user_id=<?=$user['id']?>" >Delete</a></td>

Link-urile formate sunt de tipul: http://localhost/invatam-sa-programam/delete.php?user_id=3