Assume that you have three fields named: SerialNumber, ItemName, UnitPrice.
To retrieve the details of these three fields in editable form,
echo "<table>";
echo "<form action = filename.php method = post>";
$query = "select * from ITEM where SerialNumber like ...";
$result = mysql_query($query);
$record = mysql_fetch_object($result);
echo "<tr><td>SerialNumber</td><td><input type = text name = serial value = '$record->SerialNumber'</td></tr>";
.........
echo "<input type = submit name = Updating value = 'Update Now'>";
echo "</form>";
echo "</table>";
if(isset($Updating)){
$query = "update ITEM set SerialNumber = '$serial', ...., where SerialNumber like ...";
$result = mysql_query($query);
}