PWA applications are like all mobile applications and work in exactly the same way as the applications you have on your mobile. They are available in the Play Store and App Store from where the user downloads and installs them on his mobile.
What is the difference between them and Native Applications?
A Native application is Facebook (or Airbnb, Booking, Tripadvisor etc.). This means that if you visit the Facebook site through a browser (eg Chrome, Mozilla) you will see a completely different layout, design, buttons, etc. than if you visit the Facebook application. This is because the application has been built as a separate entity to work exclusively on mobile devices.
In contrast, the PWA application presents the website but as a Mobile application. In other words, the user to see your website through his mobile will no longer need to go through his browser (Chrome, Mozilla, etc.) but will have an application permanently installed on his mobile from which he can visits your website. The big advantage is that they are made at a low cost (compared to native applications) and the visitor does not understand the difference between native and PWA. But there are other advantages: