Not quite. If you want to check whether or not the form is submitted, you'll need to give your submit button a name:
<input type="submit" name="submitbutton">
. In PHP, this will set $GET['submitbutton'] or $POST['submitbutton'] (depending on your method, set in <form>). Thus, you can:
if (!empty($_POST['submitbutton'])) {
// it's posted
}
else {
// it's not posted
}
Now, use the same method for all other fields. If you have an input field named "email," you can access it by checking $GET['email'] or $POST['email'].