Setting Up Unity for Installing Application on Android Device
Follow the steps mentioned below for Installing the Android application on your Smartphone:
Click on "File / Build Settings / Add Open Scenes". You should see something like this shown in the image below.
In Platform option, select "Android/Player Settings"
Give your Application a company name and product name and also a default icon if you want.
In Resolution and Presentation, change Default Orientation to Portrait
In Other Settings, Add Bundle Identifier in this format "com.companyName.ProductName" and select the Minimum Api Level
After completing all the Player settings, just click the "Build and Run" option (make sure your you have downloaded and installed Android SDK, specified its location in Unity and your Android mobile is connected to your PC.)
After Clicking "Build and Run" you will be asked to name your .apk file, name it anything you want and click save.
If you have any doubt or suggestion, please comment below. That would help you as well as others who read this post.