What is your model iPad? Identify your iPad model - Apple Support
What is its version system software (iOS/iPadOS)? Find the software version on your iPhone, iPad, or iPod - Apple Support
The Apple TV app will want to load content from online sources, so the iPad must have internet connectivity (e.g. Wi-Fi). The app will behave differently when offline. Also, for iPads with cellular options, the Apple TV app must have its settings to allow for using cellular data (when not on Wi-Fi); configurable per app, and (I think) that setting might be off by default.
- Settings﹥Cellular﹥[scroll down to apps list]﹥TV﹥
The modern Apple TV app is available with iOS/iPadOS 12.3 or later. It is downloadable for iOS/iPadOS 10.2 or later.
Apple Media Services (and thus Apple TV app features) are not available in all countries: Availability of Apple Media Services - Apple Support. In some countries it is just for synced videos as transferred from a local computer.