Docker is a containerization tool that has many purposes but its main pro is that it can take an application and ensure it works on legacy systems and makes it cross-platform. As long as the machine can run docker, that application will run which is why docker is used in development to containerize applications for simple deployment and access.
Quick Docker Tutorial
The fastest way to check if docker is installed correctly is to run
docker run hello-world
What this does is checks if the hello-world image is on your host machine, because this is your first time running docker the daemon will have to download the image from the docker hub. Once the image is pulled from the docker hub, it runs a container based on that image and you should see a message from docker.