Download the app to your Android device and open it. The easiest way to do it is by using Android web browser - just navigate in it to the Downloads page and download the app. Then open Downloads in the Apps screen and click on the downloaded app. The system will ask if you want to install the app. The app requests permissions to access the Internet (that should be read as a permission to provide an Internet service - web server) and to receive Boot Completed notification (to start on boot - if opted in). Accept it. That's all.
The app is completely free for personal use, however please consider making a small donation.