This depends if you are ordering multiple items from the same shop or from different shops. If you ordering from the same shop, then copy and paste the web links for each item and put them in the "item details" text box along with a description and the individual prices. In the item price box put the total price. If you want to order from different stores then you will need to place a separate order for each shop.
If you are ordering multiple item from different stores then please make sure you tick the "consolidate orders" check box. My USA partner will then combine your orders into one box (if possible) to save you money on the shipping. There is no separate fee for this service, but all orders will have the minimum shipping and handling fee.
If you are shipping economy is often makes sense to not consolidate as the saving can be minimal and it slows down the shipping of your whole order.