Basic help for radio buttons needed

Hi all, I am sure this is a very simple question, but after reading reams of doco I still can't find the answer. I am very new to PHP and HTML coding. I have a form (html) that uses radio buttons that goes to some PHP code - how in the PHP code can I tell which radio button was selected? My HTML code (which is inside another PHP page) is as follows <form action="admin.php" method="GET"> <input type="radio" name="admin_do[]" value="Add new user">Add new user</br> <input type="radio" name="admin_do[]" value="Change User password">Change User password</br> <input type="radio" name="admin_do[]" value="Delete user">Delete User</br> <input type="radio" name="admin_do[]" value="Add new document">Add new document</br> <br> <input type="submit" name="submit" value="Select" </form> I have tried various things in admin.php but nothing gives me which radio button was selected. TIA Janet