What is Docker? The 2-minute mental model

Docker lets you package an app with everything it needs (system libs, runtime, config) so it runs the same everywhere.

• A Docker image is a recipe (read-only).
• A container is a running instance of that image.
• You define images with a Dockerfile → build → run.

# Build an image from Dockerfile
docker build -t hello .

# Run it (maps port 3000)
docker run -p 3000:3000 hello

That’s it—portable apps, fewer “it works on my machine” moments.