Once you have an APK demo app it's really easy to install it on your Android device.
This will allow you to run your demo as a native app and it will even work without an internet connection.
To learn how to create the demo app APK follow this guide: How to build a native Android app demo
How it works
1 Enable Unknown Sources in your phone's security settings
Settings -> Security -> Unknown sources
2 Connect your phone to your computer using a USB cable
3 Enable Transfer Files
On the phone you should get a notification like USB for charging - touch for more options.
Tap on it and enable Transfer files.
On the computer open the File Explorer tool (like Windows Explorer on Windows and Finder on Mac), locate the phone and copy the APK file to the phone's memory (for example in the Downloads folder).
5 Use a File Manager app to open the APK file
There's no default File Manager in Android so you have to install one - our favorite is from Asus: File Manager - but any other one would do the job.
6 Install the APK file
Open the file manager app and tap on the APK file. It will request your permission and the App will be installed on your device.
That's it: you now have your app demo installed on your Android device as an APK file.