To compile and build an executable package (APK) that runs on an Android device as a standalone application, you'll need to build your project. There are different ways to do this. Here, we'll look at a method that'll work for most Android devices, even if you cannot connect your device to Unity. Firstly, access the Player Settings by choosing Edit | Project Settings | Player from the application menu, and assign the application a unique Bundle Identifier, by entering a name in the Bundle Identifier field. This is used to uniquely identify the Android application, and would also be used on an App Store.
Assigning the application a Bundle Identifier
Note
Remember, before creating your Android game, always check out the App Store submission guidelines to make sure your product will be accepted: https://developer.android.com/distribute/tools/launch-checklist.html.
Next, to build the application, select File | Build Settings from the application menu. When the Build Settings...