The usage of containers is an implementation detail and not the main point. Instead, think of it as a Distributed Operating System trying to schedule work and utilize resources in the best possible way.
This article by Nikhil Jha contains a fairly standard walkthrough of the Kubernetes architecture. However, it also contains a really good explanation of what Kubernetes is and how it differs from Docker.
Notice how my definition of Kubernetes doesn’t include the word “container”. This is on purpose. The main idea behind Kubernetes is declarative infrastructure management, not running containers.