eBay's Global Shipping Program is a great way for domestic retailers to ship internationally without a whole bunch of hassle. While the program is fully compatible with ShipStation, you'll probably want to separate out these orders so that you can make sure everything is handled appropriately.
Luckily, eBay includes a reference number on each order in the first line of the address. Because of this, you can create an automation rule to add a tag to each order to be able to easily distinguish them during your normal order processing.
First, make sure that you have a tag that you want to apply to the orders. If you don't have one, you can create one on the Orders tab by going to Tags > Manage Tags.
Head to your Account Settings (the wrench icon in the upper right).
Next, select Automation and then Automation Rules from the sidebar on the left.
Now, click the Create Rule button.
Here, name your rule and then select to "Only apply these actions to orders that match specific criteria." Then, select the following criteria:
Next, select Add an Action. Choose to Add a Tag... and the tag you've made for GSP.
When you're done adding any other actions you wish to happen on your eBay Global Shipping orders, remember to Save your changes. Now, whenever you import new orders that apply to that filter, the app will do whatever actions you specified automatically.