your orders page should have a link to the order detail page that sends a querystring variable of the OrderID to show the details for.
OrderDetals.php?id=4
for example.
the recordset on the order details page should contain a where clause to filer the orderID column on the id querystring:
I am attaching screen shots to demonstrate how the recordset should be configured.
This is also covered in the "Creating an Order History page" tutorial on the eCart support page:
ecart/