The important concepts aren't that complicated.

Instead of nesting a computer (VM's) the operating system makes the program think it's on its own dedicated computer (isolated file system space, cpu, and memory shares). A Dockerfile is just a basic script to construct one of these computers by commands and files.

The real reason people get excited is because they can ship a Docker "image". It's a layered filesystem which really is just like saying there's a system tracking who puts what files in what place and so it's easier to just send the whole setup to someone then try to document how you should set all that stuff up to run their software.

This is "dummier" proof than the pre-existing convention of just using a package manager to do this for you.