APKs are Android Package Kits or files that help you install apps. Many Android users download APKs because the apps aren't released yet, or they provide more functionality and freedom than the monitored apps in the Google Play Store. Unfortunately, some apps promote illegal pirating activities, which results in them getting taken off the app store. If you're trying to recover an APK, it's best to do a Google or DuckDuckGo search for the missing application or one similar. Once located, download it and set it up like any other APK file.