As the final step while making a purchase of NHL LIVE™ within the NHL app, you will be asked to sign in with your login or to create a new login. By doing so, you are making a connection between your in-app purchase account and another email. This is important because this new login enables you to stream live hockey games on all supported devices, rather than just on the devices supported by your in-app purchase.
Remember that you can always create a login later to make the connection and watch on other devices. To do this, start up the NHL app and go to the Settings section then sign in. More information can be found here.