MongoDB University has many free and easy to follow courses that you should take first.
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M001: MongoDB Basics
Level: Introductory
Fundamentals of MongoDB: connecting to a MongoDB Cluster, using MongoDB Compass, MongoDB's document storage model and principles of flexible schema design, basic architecture of MongoDB clusters, CRUD operations. -
M040: New Features and Tools in MongoDB 4.0
Level: Introductory
This is a continuing education course that covers new features and tools released with MongoDB 4.0. In a series of 9 chapters, we will explore all the new functionality available with 4.0 including recently released features in Atlas, Compass, OpsManager and the BI Connector.
Introduction to the MongoDB and Mongoose Challenges on freeCodeCamp
https://www.freecodecamp.org/learn/apis-and-microservices/mongodb-and-mongoose/