Docker is a platform for developers and sysadmins to develop, ship, and run applications using containers. It allows building applications from components and eliminates friction when shipping code, allowing code to be tested and deployed to production quickly. Docker consists of the Docker Engine for building and running containers and Docker Hub for sharing container images. The document then discusses containers on Windows, how Docker works, building and running container images locally and remotely, Microsoft tools for working with Docker, and deploying multi-container applications on platforms like DC/OS Swarm and Kubernetes.