Docker is a rapidly evolving facility with great utility. An excellent way to get started learning about it is using a building block process. This also allows you to learn the real world use of it by finding a way to use it for actual tasks that you have to perform.
Here is a simple example of this that you may find helpful: you are not running Linux but want to run something that is available on Linux.
A practical case for that might be where you are unable to install a useful utility on your machine due to availability or restrictions. You could instead use Docker to temporarily run a Linux container and not change the actual state of your machine. This assumes that you already have Docker installed and working. Note that for this example we do not need to use a Dockerfile as we will only use an already existing public Ubuntu Linux image.