If you have the 4th generation Apple TV or later, you can download Apple TV apps from the App Store, just like you can with an iPhone. The first three versions didn't allow this.
Apple TV How to Download Apps – Apple TV Can't Download Apps – Apple TV How to Add Apps and Channels
If you have a 4th-generation Apple TV, which Apple introduced in September 2015, or an Apple TV 4K, also known as the 5th-generation model, which launched in September 2017, you can download Apple TV apps on it.
These versions of the Apple TV are based on the idea that apps are the future of television, as Tim Cook said when introducing the 4th generation model.
Installing apps on the 4th or 5th generation Apple TV is similar and just as easy as installing them on an iPhone or iPad. The operating system that runs on Apple TV, called tvOS, is slightly different than iOS, so the steps to install apps are also slightly different.
