The hardest part of learning this isn't any single idea. It's that six unfamiliar words arrive at once and nobody says which contains which. Here is the map. You don't need to memorize it; you'll build the real understanding by doing. But it helps to know roughly where you're going.

Start with the thing at the center: a CONTAINER is one running program, wrapped so it can't see the rest of your machine. That's the atom. Everything else is either how you make one, or how you manage a lot of them.

An IMAGE is the template a container is made from: a frozen snapshot of files plus a startup command. Images sit on disk. Containers run. Same relationship as a recipe and a meal, or a class and an object.

A REGISTRY is a shared place to store images, so a machine that has never seen your code can download and run it. Docker Hub is the public one; most companies run a private one. This is how an image gets from your laptop to a server.

DOCKER is the tool that builds images and runs containers on one machine. When you type `docker`, you're talking to it. It handles a single computer and has no opinion about anything beyond that.

DOCKER COMPOSE is a small step up: one file describing several containers that should run together, on one machine. This project uses it: eight containers, one file, one command. Compose is where most people stop, and it's genuinely enough for a lot of real work.

KUBERNETES is what you reach for when one machine isn't enough, or when you need the system to repair itself without you. You stop saying "start this container" and start saying "three copies of this should always exist." Kubernetes then makes that true, continuously: restarting things that die, moving work off machines that fail, and updating without downtime. A POD is its smallest unit: usually just one container, plus the bookkeeping Kubernetes needs.

One sentence for the whole map: Docker builds and runs containers on one machine, Compose runs a group of them together, and Kubernetes keeps a group running across many machines even when things break.

You'll do all three in this course, in that order, which is also the order they were invented, and the order in which each one's problems make the next one make sense.