At the risk of oversimplifying, you can use Docker wherever you might want to use a full-fledged VM. You can use it to run a job, host a webserver or any other scenario that you can think of. What makes Docker (rather containers) different from a VM is the way it sandboxes all your application's dependencies into an isolated sandbox.

So let's say you have a python app that for relies on a dependency that needs C bindings (e.g. ImageMagick). Instead of running `./app.py` freshly downloaded from some Git <repo>, you would run `docker run <repo> ./app.py`. In the former case, you would need to care of, say, the C dependencies. In the second case, they are packaged in the image that Docker will download from <repo> prior to run the ./app.py process in it. (Note that the two <repo> are not the same things. One is a Git repo, the other is a Docker repo - called an Image.)

Think of process of the building a container as taking a snapshot of the entire OS (such as VM images) but w/o the high overhead of running these images.

Feel free to reach out to me if you need more clarification!

If you're working on multiple projects simultaneously (e.g. multiple microservices within a company or multiple client projects if you are a freelancer), Docker is a godsend to quickly get your development environment setup. All you need to declare your "infrastructure" (e.g. PostgreSQL, Redis, etc.) in a docker-compose.yml and `docker-compose up` will get you up and running in no time.