Google Play Store is Google's app store. Amazon's tablet runs a version of Android that replaces the Google Play Store with Amazon's own store... while it has a very good selection of apps, some key ones are missing, most prominently anything released by Google themselves (YouTube, GMail, etc). That said, the Google Play Store and other Google Apps can be installed on the Amazon Fire 5th Gen with a small bit of work (linked to previously), at least until Amazon patches/updates the software to prevent it.