"Works on my machine" is the most expensive sentence in software. Docker exists to kill it. At its core, Docker packages your application together with everything it needs to run — the runtime, libraries, and system dependencies — into a single portable unit that behaves identically on your laptop, a teammate's machine, and production. Once the concepts click, it stops feeling like mysterious DevOps magic and becomes a tool you reach for daily.
Images and containers: the core idea
Two words do most of the work:
An image is a blueprint — a read-only snapshot of your app and its environment, built from a Dockerfile\.
A container is a running instance of that image — a lightweight, isolated process.
