For mastering the fundamentals
You can also get a hold of his book — Pro MERN Stack — for a more thorough, and detailed coverage of the fundamentals, and the corresponding tooling in the ecosystem; and handy exercises at the end of each chapter to cement your understanding of the said topics.
For the "real-world" experience
Once you're comfortable with the fundamentals, you can move forward to improve your skills by building real-world projects. This will help you in addressing the problems that most apps face in their infancy to get "production" ready
- how to properly structure your app
- when should you use a certain technology
- how to efficiently bundle your application and make it ready for deployment, etc...
Here are a couple of example projects (and tutorials) that you could use:
Once you get here; you can use a boilerplate like mern.io, for an opinionated take on the best way to structure a MERN application; and you either start using it, or fork from it to build according to your needs, and ideas.
Hope this helps! :)