Google intends to make websites more interactive on it mobile OS Android and it hope to achieve that with it Web APKs.
Google had released new version of Chromium for Android that now allows us to download web pages but here called Progressive Web Apps. In other words, Progressive Web Apps are websites that uses a more sophisticated UI. They uses animations and are display in full size making them look more like Apps than web pages. Google uses it weather card as an example. As you can see it transits from a
chrome-like- widget to an Android-like- app.
Now talking about Web APKs, they use the same principle as Progressive Web Apps but with much more improvements. Their codes can be directly integrated to the phone's code thus pushing their integration further. They can have access to some parts of the phone that the browser doesn't have and the icons can be directly install on the home screen allowing us to launch them without having to open the web browser. This makes them look more like Android Apps.
For now there exist No Web APK but there exist some Progressive Web Apps that can be use offline. You can have an idea of how they work by going to pwa.rocks that contain à bunch pf them.
The real goal of web APKs is to provide services in a more confortable UI. With this, the websites won't have to load completely bust just the services they have to offer such as a currency converter thus increasing the download speed.
Web APKs have been thought to work instantly on a limited environment such as chrome. We can therefore imagine that they are light weight and ressource efficient therefore embody Google's wish to make the web more simple of use.