Any learning suggestion for the MongoDB Java Driver?

Hi MongoDB community, I’m a Java developer and I recently got my MongoDB Certified Developer certificate. But I want to learn more about the in-depth knowledge of MongoDB, so I pulled down the code of Mongo Java driver from GitHub - mongodb/mongo-java-driver: The Java driver for MongoDB. The things is there are some many classes, any suggestion where should I get started as an entry point ?

Enjoy M220J: MongoDB for Java Developers | MongoDB University

I was too quick. I imagine that since you got

you already took M220J.