If you want to build a fully functional online store you will need to use the eCart extension, and most likely also use the Data Assist and Security Assist Extensions aswell.
The eCart Extension will give you the shopping cart functionality, along with payment gateways. Data Assist will allow you to develop a back end facility where you can add / remove / update products, orders and customer details and Security Assist will allow you to have a customer login facility during checkout.
You may also want to consider CSS Form Builder for emailing order receipts and maybe even Form Toolkit if you want to use Captcha and Datepickers as part of your ordering process.
To create a page with thumbnails that link the the product page you simply provide a standard HTML link with a URL variable e.g
http://www.mywebsite.com/product.php?id=<?php echo ($row_rsproduct['prod_id']); ?>
This tells the link to go to the product.php page and send a URL variable that contains the unique product ID for the requested product.
On the product detail page your recordset then needs to filter the products by the name of the URL variable (in the above case this is called id)
An online store can be as simple or as complicated as you want to make it.
Hope this helps.