Step 1: Create a PWA
Sign up for Progressier and follow the instructions to add an app manifest and service worker to your web app. You can also do this manually but Progressier will save you a lot of time and effort.
Step 2: Create app store bundles
Next, you'll need to create bundles and upload them to the stores. This is where PWABuilder comes into play. PWABuilder allows you to ship your PWA to the app stores. Simply sign up for an account at PWABuilder and follow their instructions.
A word of caution...
While technically possible, wrapping PWAs for the app stores is not recommended. It's a bad technical solution that creates more problems than it solves.
PWAs work much better when installed from the browser (which is what Progressier is designed for).
Here is a non-exhaustive list of problems you're likely to encounter when your app is wrapped from the app stores with PWABuilder:
Push notifications won't work
Apple/Google may require you to integrate their in-app payment solution and pay them a commission on your in-app sales
Third-party login options (e.g. sign in via Google) may break
Apple/Google may reject your app or ban it from their app stores anytime
Advanced web capabilities (e.g. Bluetooth, NFC, etc) will need to be rebuilt from scratch in the native wrapper