Google Installer is an app that let you easily install the Google Play Store in your Xiaomi smartphone. To do so, the app lets you comfortably download and install these apps: Google Services Framework, Google Account Management, Google Play Services, and Google Calendar Synchronization. Once all these apps have been installed, you can install and start using the Google Play Store. 

Google Installer is an app that can only be used if you have an Android Xiaomi smartphone and none of the above mentioned Google apps are currently installed. In fact, if you have one of the apps installed or you're just missing one of them, you may have to uninstall them beforehand and then complete the process.