With the presentation layer pixel-perfect to the design, and the props & bindings setup, you are now ready to export the code components. To do that, click the download icon at the top. You will download a zip file with assets folder and two .js files - Card2.js and useCard2.js.
Card2.js is the presentation aspect of the module representing the visual design. You do not need to edit this file. If an updated design is synced, this code is update automatically. So your designer can iterate with little or no developer intervention.
useCard2.js is the hook. It has the stub for your custom code. You can call your backend APIs or add any business logic.
After you add your custom code, you can now add the component to your react app in the appropriate location and run it.