App
If you're using a Progressive Web App-compatible browser (for example, Chrome), installation might be as simple as clicking an "Add to homescreen", "Install", or similar popup button. If no such button presents itself, you might be able to find a similar command in your browser's settings menu (this is the case in, for example, Safari on an iPhone).
The PWA via the Google Play, Apple App, and Windows Stores will be coming soon to a computer near you ... Well, hopefully ... Clank, Rattle, Puff ... It's a work in progress.