This editor extension lets you install already created .apk builds directly from Unity to your Android device. Unity has only "Build" and "Build and run" options, this editor script provides you with an option to "Run" previously created build without building new one. This feature makes development easier if you have multiple .apk builds that you need to switch often on your Android device. You need to have installed Android SDK (they come with Unity). Connect your Android device to PC via USB (wireless is not supported, multiple connected devices at once are not supported) and navigate to Tools - Install APK. Choose .apk that you want to install. This utility should work on your PC seamlessly if you can "Build and Run" your project for Android platform.