The Android TV platform is an adaptation of the Android OS for set-top boxes and as integrated software on smart TV hardware. Its home screen uses a vertically-scrolling, row-based interface, including a "content discovery" area populated by suggested content, followed by "Watch Now" rows that surface media content from installed apps.
Some Android TV doesn't have Google play store but still you can download any android app in your TV.
Method 1: USB Drive
Take a backup of any app from any android mobile. copy .apk file in USB drive and open in android TV to install it.
Method 2: App Store
Method 1 is long way there also a option available best replacement for Google Play Store is Aptoide TV app. Download it to your Mobile or Laptop/PC from here.
and copy to USB drive. Change the settings in your Android TV to "install Apps from unknown sources" . Usually this will be under settings >> security settings Plug in USB drive and install Aptoide TV App and have full access of unlimited Android Apps.