Integrate simple chat app to any website? [on hold]

I'm starting a project to create a simple chat app in reactjs, im still at beginner level and don't know alot of things about web. After successfully creating an app I want it to link/integrate it into 3 to 4 websites

Where I give those websites some kind of plugin/code and they can Integrate it into there website.

App will be used to chat with website visitor, like customer support app at the bottom websites.

To do all these things by my self, I'll need you guys to point me in right direction to where to look. Books, tutorials, which libraries and framework to use etc.