If you have a unique ID for each order (an Order Number), you should assign the checkbox with that ID so that you know which order it is with:
i.e.
<input type="checkbox" name="cb" value="<?=$Order_ID;?>">
Then, when you process the form, you should be able to test for:
if($cb!==""){
// the box is checked
print $cb;
// displays the Order ID to be deleted
}
good luck! roki