When creating a Store Item, if it is a physical item that requires delivery, selecting the correct item category will give you the option to add a shipping cost. You can turn on both domestic and international delivery options and set separate prices for each.
Keep in mind that the shipping cost is subject to the 80% payout amount for Store Items (see our payout percentages here) so you'll want to factor that into your calculation; for example, if you require $7.99 to send your item, you should set your shipping price at $9.99.
You'll want to make sure that you base your shipping price on the item being shipped as the weight and size can effect the shipping cost, along with packaging and stamps required. Your best source for information on how to determine the shipping cost of different store items will be whichever mailing service you plan to send your package through.
Providing a tracking number for your shipped item can give you an extra layer of protection should there be a purchase dispute or if the member claims the item was unreceived, so if you plan to add that, make sure to factor that in as well incase there is an associated cost.