You can be logged in both devices you're using at once. So if you have an iPad at your drive-up window and your dining room, you would just need to sign into each with your account information, and all payments would go to your account.
That's the simple setup, but from there you can get a little more complex, depending on your business needs. For example, you can enable Employee Management features that allow you to track sales and setup register permissions.
Let me know if there is anything I can help clarify!
