This process works differently, depending on which model of Apple TV you own.
How can I tell which Apple TV model I own?
Apple TV (3rd gen)
This model comes with a small silver remote and there is no way to add apps to it.
Latest Apple TV (4th gen)
This model comes with a remote that has a trackpad on the top part, and has access to Apple's app store.
You should be able to find photos of the models here: http://www.apple.com/tv/compare/.
Apple TV (3rd gen) route
Contact firstname.lastname@example.org and provide the email address used to create your account online.
Apple TV (4th gen) route
On your computer, go to www.tastemade.com, and sign in with your account.
2. On your Apple TV, to go the Tastemade app.
3. In the Tastemade app, go to Settings > Activate Device. This should display a code on the screen.
4. On the computer, go to www.tastemade.com/activate. Enter the code shown on the TV screen, then click on the Activate button.
5. On your TV, click on the Activate button at the bottom of the screen.