<?php
if ($submit = 1) {
// process form
$db = mysql_connect("localhost", "root");
mysql_select_db("mydb",$db);
$sql = "INSERT INTO employees (first,last,address,position)
VALUES ('$first','$last','$address','$position')";
$result = mysql_query($sql);
echo "Thank you! Information entered.\n";
} else{
// display form
?>
<form method="post" action="<?php echo $PHP_SELF?>">
First name:<input type="Text" name="first"><br>
Last name:<input type="Text" name="last"><br>
Address:<input type="Text" name="address"><br>
Position:<input type="Text" name="position"><br>
<input type="Submit" name="submit" value="submit">
</form>
$submit = 1
<?php
} // end if
?>
</body>
</html>

<?php
if ($_POST['first']!='') {
?>
mostrar formulario
<?php
} else {
completar base (recuperando los valores del formulario mediante $_POST['first'], ...)
 }
 ?>