Nick here from Shopify. Really good question!
When using dropshipping services such as Printful and Oberlo, you would set up the shipping rates in your store admin (Settings > Shipping). You can distinguish the different shipping costs for each country such as USA and China by setting up different shipping zones. You would also need to decide if you want to charge by price or weight for your shipping. Shopify has a guide on how to set up manual rates in detail here. Once you have set up the shipping zones and decided how you're going to charge for your shipping you will need to set up the rates.
Both Oberlo and Printful have guides on how to set up your shipping settings for each which you can see below:
Printful also has a YouTube tutorial which might also be of interest to you.
If you have any other questions about this, don't hesitate to reply and ask!
All the best, Nick