Actually, this step is very simple. Just run:
$ npm install
$ npm start
or
$ yarn
$ yarn start
There you go!
When you want to push some code, don't forget to check your CI tests. You can launch the process with
$ npm test
or
$ yarn test
An important thing is to keep a good coverage for the app, so when you update some code, be sure to update the test that comes with it.
And you're done. Have fun!