React js file changes not updating on browser window

Newbie to React… Most tutorials about React assume you are using your localhost. I’m trying to edit on an actual website (testing subdomain). So that when I’m actually building a website I’ll have all the steps down. I copy index.html and index.js with the inline react library files from Bob Ziroll 's tutorial into a folder on my server under public_html, and I can view the result in the browser. But any subsequent changes to index.js do not show up in the browser no matter what I do or how many times I refresh the browser window. Have also tried to install npm (not sure of all the steps to regurgitate here, but it worked) on a new application on my Cloudways hosting platform. I can see the basic Hello World version. But again, any changes to App.js are never reflected on the screen. Which is frustrating because every tutorial shows that any minor change immediately updates on whatever local host or scrimba window they’re using. What am I missing (that no tutorial ever covers)?