Where does the script for sessions go in the widget configuration?

I’m following the Okta Authentication Quickstart Guides, on Okta Sign-In Widget. It says to ‘copy this widget configuration into your front-end application:’ and gives a script. what is it referring to as the front-end? what file specifically will this go into? app.js? loginPage.js?

The script is not in the app yet. After attempting to sign in this error is givein
Failed to load https://dev-827074.oktapreview.com/api/v1/sessions/me: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access.

Make sure that you add http://localhost:3000 as a trusted origin: