I combine shipments within the United States (discounting the shipping costs) for items made with one payment.
In other words, put your items in your cart and make one payment.
Shipping is never more than $4 no matter how many items you purchase with one payment.
INTERNATIONAL SHIPMENTS are handled differently. You are going to pay more than $4 shipping. You can put your items in your cart and make one payment, but eBay doesn't combine shipments to outside the United States. For EXAMPLE, if you purchase 6 items, I'll receive $24 ($4 x 6) to make 6 shipments to eBay's hub. eBay will put international shipping labels on the 6 shipments and send them to you. I never see the cost of the international shipping labels (which can be a lot more than $4) and never handle that money. You are paying eBay for those labels.