Installing
Visit Docker's documentation installing Docker engine on Ubuntu for instructions on how to install the very latest version, including the Docker GPG keys. You can also install Docker from Ubuntu's own package repositories via
sudo apt install docker.io
Dockerfile
The environment inside of a Docker image is defined by the instructions that the Docker image builder picks up from a file. The default expected name for this file is Dockerfile. If your Dockerfile has a different name, you need to provide that file name to the build command:
docker build -t MyImage -f /path/to/MyDockerFileName
The Dockerfile Reference describes the commands that can be issued in a Dockerfile