Turn on your Apple TV and sign in with your Apple ID
Open the App Store on your Apple TV
Search for the app you want to add
Select the app from the search results
Choose Get or the download icon
Enter your Apple ID password or use Face ID/Touch ID if prompted
Wait for the app to download and install
Open the app from the Home screen
To add apps you already bought, go to Purchased in the App Store and download them again
To update apps, open the App Store and check for available updates
To delete apps, highlight the app on the Home screen, press and hold the touchpad or clickpad, then choose Delete