Paste your site in the builder
Build a demo APK first to try it on your phone; Builder Pro builds the full app and the AAB.
A store app, from the store you already run
Your Shopify theme, products, prices and checkout are all reused: the app loads your live store, so new products and price changes appear straight away. What the app adds is a home-screen icon, native tabs and push notifications.
Tabs that sell
Shopify's paths are the same on every store: /collections/all for the catalogue, /cart for the cart and /account for orders. Make them three bottom tabs and the store navigates like a shopping app. Other platforms have equivalents; open them in your phone's browser to find the paths.
Push notifications
With OneSignal set up in the builder, announce sales, new drops and restocks to everyone who installed the app. Keep it to one or two a week; shoppers uninstall apps that nag.
Payments
Checkout works as it does in the mobile browser. Wallets that need a browser redirect open the payment page and come back. Test a real order on the demo APK before you subscribe.