Entering text on the newest Apple TV got much easier with the recent release of tvOS 9.2 Users can now use their voice, with Siri Dictation to spell out usernames and passwords, or tell Siri what to search for.
Additionally, Apple added the ability to pair a Bluetooth keyboard to the fourth-generation Apple TV. With a keyboard paired, users can enter text and navigate the TV's interface. If the following instructions aren't working for you, make sure you've updated your Apple TV to the latest version of tvOS by following these instructions.
Start by placing the keyboard in pairing mode. The process will vary by manufacturer, but typically involves holding in the pairing button for a few seconds. Next, open the Settings app on your Apple TV, then scroll down and select Remotes and Devices. Under the "Other Devices" section, select Bluetooth.
The Apple TV will begin searching for visible Bluetooth devices. A list of nearby devices will be displayed; scroll down and select the keyboard from the list of nearby devices. If prompted, enter the pairing code. If you don't know it, try 0000 or 1234; if that doesn't work, you'll need to reference your keyboard's manual.
With they keyboard paired, you can now control your Apple TV and enter text. Use the arrow keys to navigate, Return to select items, and Escape. An Apple knowledge base article doesn't go into too much detail about keys and their purpose, but in my experience if you pair an iPad keyboard to the Apple TV the shortcut buttons more or less mimic the same functionality you'd expect on an iPad. For example, the home button takes you home, while the music controls will pause, play or skip songs. Experiment with the controls and buttons on your keyboard to learn what, if anything, they do when connected to your Apple TV.
Otherwise, you can type in any text field to speed up searches or entering log-in credentials, as well as start typing the name of a movie of music artist to jump to the respective section when viewing your personal library.