How to recognize new subscribers and then change their status

Thanks to your direction, I am making progress on this. I have successfully set up the Twitch API Authentication index.js using Node, Express, Passport and the requested Scopes. Based on the output from that, it seems it is correctly set up as it is returning the ACCESS and REFRESH tokens. I also have have an app.js file which is also monitoring Port 3000.

Because this is my first time doing this, I am stuck on where to go next. In particular, where should my js code go that will monitor chat and do what I need it to do. In app.js? In index.JS? neither? I don’t know how to connect all this together and start the bot so it does the appropriate interaction with chat. An pointer to an example app would be helpful if it exists.

Thank you for helping guide this “first timer” through this process