How to start the debug server?

Question

React

I'm trying to make an extension for chrome.
I try ready-made templates from github, they work. But I don’t understand how to start the usual debugging in the browser on localhost:3000? like a normal react application?
The readme says the following.

git clone this repository
Install dependencies using yarn (or npm install if not using yarn)
Run yarn:dev to build the extension and start watching the src folder for changes

https://github.com/Gyumeijie/react-chrome-extensio...
Tell me how to use such projects? I translated but did not understand.