Concept of XComs can be described much more simply, we don’t need to bother additionally with creation of sensors, operators and stuff like that which are not the topic of this lesson… Why?.. It just make the concept of XCom much harder to understand, because so much is in the way.
For those who also stumble upon it, an example of much simpler explanation - https://betterdatascience.com/apache-airflow-xcoms/
More detailed but still more or less clear - https://marclamberti.com/blog/airflow-xcom/
Course: An Introduction to Apache Airflow - Learn Interactively
Lesson: https://www.educative.io/courses/introduction-to-apache-airflow/xcom