Hi,
Basically the action would be the page where you have the script which willd o the database querying:
<form action="insert.php" method=post>
<input type="text" name="firstname">
<input type="submit">
</form>
insert.php:
<?
// .. $database handles
$firstname = $_POST['firstname'];
$insertquery = "insert into mytable (firstnamecolum) values ('$firstname')";
$result = mysql_query($insertquery);
?>
J.