What is docker? For that matter what is a container? Find out here.
Docker is a container runtime, ultimately run on containerd. Docker is a packaged and more user friendly version with a graphical interface as well as a command line interface suite. Although it has many challengers and potential usurpers, docker remains the go-to tool for containers.
An oversimplification is that a container can be thought of as a much smaller VM. In general VM's require virtualization at the hardware level, hosts an entire OS complete with it's own kernel. A container on the other hand can share resources with it's hosts, leverages user-space a bit better, and can often run only what is necessary for the application. Ultimately, a container is more portable, and consistent than a VM and helps to eliminate the "it worked on my machine" issue.
First you'll need to install docker to ensure docker has installed properly you can run your first container with.
This will take you through the official guide for docker, and truthfully it's a great tool! It should be accessible via localhost in your browser.