A container is just changes you make to a file system to get something running. To run a container, Docker applies changes listed in its image then executes its

A container is just changes you make to a file system to get something running. To run a container, Docker applies changes listed in its image then executes its entry point. When it stops, changes to file systems are preserved but memory is not. When removed, everything is gone so next time it runs you're starting fresh from original image. Magic with container are: 1) those changes are only visible from code running in the container, and 2) changes can be layered on top of each other (FROM in Dockerfile).