The step by step approach for using this repo has been described in the medium article OAuth using MEVN Stack. Please give it a read to learn how to use PassportJS in a RESTful MEVN app.
In order to have it running, be sure to have npm, node.js and mongodb installed in your system.
Follow the steps to get your own ClientSecret and ClientID and relace it in the following file:
/server/config/passport-setup.js
If you have any queries or suggestions for improvement, you can message me in twitter at @rkpattnaik_780.