Think of a ship dock, which full of containers, thousands of them. Each of them contain different things, in a fantasy term different world. Docker is something like that.
It is a developer tool which help us to run applications in an isolated environment, where you can start a service, app,local host, MySQL, SQL server, mongodb etc and some of them can communicate each. It’s like a VM , isn’t it?
You need not to install many database on system any more , use a docker container and still can access with workbench.