Each camera has its own paid subscription. But you can manage all of your cameras and pictures from the same account and app. In addition, two cameras, each on the same plan level (e.g. each with a paid Outfitter plan or Pro plan subscription) can share data with each other, so if one goes over its limit, it can use unused data from the other camera.
To activate your second camera, simply click the ADD CAMERA button in your mobile app.
Or the ACTIVATE NEW CAMERA button on the web app.