To connect your OpenSky store to ShipStation, you'll first need to reach out to OpenSky at shipstation@opensky.com so they can provide you with the necessary credentials. Once you've received the credentials in a response, simply follow the steps below in ShipStation to connect the store.
Head to your Account Settings (the wrench icon in the upper right).
Next, select Selling Channels and then Store Setup from the sidebar on the left. 
Then, click on the Connect a Store or Marketplace button.
Search for or find and select OpenSky from the list of logos
You'll need to enter the UserName, Password, and OpenSky URL which was provided to you by shipstation@opensky.com. After you enter the credentials, select Test Connection to verify the information is correct, then hit Connect to create the store connection in ShipStation.
Note: If you use OpenSky to manage your Groupon Goods orders please contact support so they can load in the Groupon Goods' custom packing slip template. They can also assist you in setting up automation rules to better manage the cross-channel orders.