While loop Mysql updating checkboxes where to start

I have a question how can I update the database if person uncheck or check a checkbox and update the boolean field in mysql? For days stuck with this problem, because problem I don't know how to make a form or check if it is validate inside of a while loop here is my code:

<?
$result= mysql_query("SELECT * FROM cars");
$counter = 1;
while($row = mysql_fetch_array($result)){
    echo '<tr>
        <td>' . $counter++ . '</td>
        <td><input type="checkbox"';  
        if ($row['show'] == true){  
            echo 'checked></td>'; 
            }else 
            { 
            echo 'unchecked></td>'; 
        }
    echo '<td><img src="../xml/'.$row['cars_id'].'-1.JPG"  width="120px">
</td>';     
    echo "<td><h3> ", $row['brand']," " . $row['model'], " " . $row['type'], 
" &euro; " . $row['price'], " </h3></td>";
    echo '</tr>';
 }
?>

p.s. I am aware of the mysql to mysqli or pdo but it is a HUGE script...