An installable icon will appear but this will look different depending on your browser, a few examples have been listed below:
After locating the correct icon, click on it, then click on Install
An icon for the app will be added to your desktop and will look like the one below:
Even if Safari isn't the default browser on your device, you must use Safari to install the PWA.
Click on the link:
https://iitoneloc.github.io/trashscan-app/
Click on the share icon located by the address bar:
Click on Add to Home Screen:
Click on Add to confirm
For chrome based browsers you can refer to google's documentation as I do not have an Android device.