A Dockerfile works in layers. These are the building blocks of Docker. The first layer starts with the FROMkeyword and defines which pre-built image we will use to build an image. We can then define user permissions and startup scripts.

In Docker, a container is an image with a readable layer built on top of a read-only layer. These layers are called intermediate images, and they are generated when we execute the commands in our Dockerfile during the build stage.