Next step, create an account on dockerhub. That will allow you to download docker images to play with as you learn docker.
The documentation on docker’s site is quite good. That’s how I got started with docker. I can also recommend Linux Academy, they have several docker courses.
If it helps, think of docker like vm’s. You can create and delete containers. Once a container has been created, it can be started and stopped. You can define persistent storage, and any special network configurations for containers. Just like you can a vm.
There are two parts to Docker. Docker, and Docker Compose. It is run from the command line.
Docker is the main application, and Docker Compose is what launches the Docker images.
To launch a Docker image, you would type “docker-compose (image name)”
I would suggest you get Docker-CE and Docker Compose off Git Hub, than use the ones in your repo.