Docker provides a way to run applications securely isolated in a container, packaged with all its dependencies and libraries. -the official Docker documentation
Simply put, Docker is a platform to build, run and even share so called containers. A container consists of an operating system (usually a Linux distribution) and some software to perform a certain (set of) task(s).
This Wikipedia article might be a readable summary of what Docker is and can do. Alternatively, this website tries to offer a simplified tutorial like introduction to Docker for beginners (just read to introductionary chapter to get a basic grasp of what Docker is and can do, skimming the first chapter should give you a basic introduction to some phrasing and concepts).
Follow the instructions for your operating system here.
Operating system specific configuration steps are covered in the installation instructions.
Docker comes with a rather large set of options and posibilities, all neatly described in the Docker manpage and the (again, rather large) Docker documentation.
When trying to use a dockerised version of an application or trying to use a Docker image downloaded from the internet, you should have received instructions on how to properly start this container.
Usually, you will be able to download a container using the 'get' command:
docker get [url]
When you are writing and distributing your own Docker container, image or Dockefile, make sure you don't only read the docs, but also write the docs; at least supply a way to start a container in the way you intended and ensure that you at least supply your intended way of building from your Dockerfile.
Note: It is very likely that your container will end up in a Kubernetes cluster.
Use the Ubuntu base image.
If you did not already do so: find out how to install Docker and get and run the hello-world container. This can be done through the docs.
Try to run the ubuntu Docker interactively (have Ba(sh) open in an Ubuntu container and try some basic Bash commands).
Write a Dockerfile, that uses the previously used Ubuntu image as its base image for a container that simply runs:
echo hello!
Go through all the required steps to get your 'hello!' container running.
Write a simple Python 3 script called hello.py:
print('python!')
Write a Dockerfile that installs Python 3, copy your hello.py into your Docker image and build and run.
If you are up for a tougher challenge, try to do the previous exercise using the latest alpine (google it!) image as base image.
If you managed to go through all the steps above and went through the Docker documentation, you now have a basic understanding of how Docker containers work.
If you lack experience with Linux or computers in general, be sure to come back to this tutorial and the Docker documentation as you learn.
Aim to go through Docker's full feature set, Docker is heavily documented and usually rather obvious.
Remember: Docker might seem like a lot and complicated, but the tricky part of Docker is learning about Linux and programming, not Docker.
After you have learned the basics of Docker, this website will give you a nice curriculum on how to build and deploy distributed applications.
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