Basic SQL query question

I realize this is really basic, I'm learning as I go.

I'm trying to make a simple page to add data to a database. The database is named 'php', and I have a table with: id (int, auto increment) and text fields named lastname, firstname, org, cdate and notes.

My form input is a quick table, the inputs look like this:

<td width="100">Lastname</td>
<td><input name="lastname" type="text" id="lastname"></td>

So I assume that's posting "lastname".

I've defined these variables to grab the post data:

$lastname = $_POST['lastname'];
$firstname = $_POST['firstname'];
$org = $_POST['org'];
$cdate = $_POST['cdate'];
$notes = $_POST['notes'];

And here's my query:

// Add the info
$query = "INSERT INTO users (lastname, firstname, org, cdate, notes) VALUES ('$lastname', '$firstname', '$org', '$cdate', '$notes')";
mysql_query($query) or die('Error, insert query failed');

Which as you can guess, doesn't work. I'm reading and googling, but right now I'm kind of stuck at this point and not sure what I'm missing. If anyone could enlighten me, I'd really appreciate it.