The store will calculate the appropriate shipping fees, using whatever modules you've configured in your store, once the store knows the customer's address. The store won't know the customer's address until the customer supplies it. There are 2 ways to do that: create an account, or start PayPal Express Checkout to login to PayPal and choose a funding source and be returned to the store to calculate the final cost of the order.

Nothing special to configure, other than making sure your store actually supplies appropriate quotes for those "overseas" addresses.