Container images are built in layers. This allows for shared layers between images and lower actual storage on device.

Images are typically created using dockerfile

In a docker file, each line starts with a command, followed by params.

Some of the most common commands are -

1. FROM - specify the base image
2. RUN - run a command inside the container
3. COPY - copy files into a container
4. ENV - specify environment variable
5. ENTRYPOINT - initial process for the container
6. CMD - default params for the initial process

docker build can then be used to build the image.