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World D0: Start Here

It works on my machine

You will learn: why an app that works on your laptop breaks on another, and how containers fix it.

Checked with Docker Engine 29 on 31 Oct 2026

The problem

Your shop app runs fine on your laptop. Mei runs the same code. It crashes! You say: “But it works on my machine!” Why did it break?

Watch

Every kitchen is different. One stove is gas, one is electric. One has no sambal. The same recipe tastes different. Git copies your code. What does it leave behind?

Drag a card into a box. Or tap the card, then tap the box.

      Watch

      Your laptop~

      • No open hatches

      Lunchboxes (containers)

      • No containers yet

      Frozen packs (images)

      • alpine:3.221 layers · 12.9MB
      • nginx:1.30-alpine8 layers · 93.5MB

      Pack the dish with everything it needs in a sealed lunchbox. That is a container: A sealed lunchbox that holds your app and everything it needs.. docker run opens a fresh lunchbox and starts the app inside.

      Try it

      What goes into the lunchbox? Swipe right to pack it. Swipe left to leave it out.

      Swipe right for good, left for needs work. Or use the buttons.

      1 / 5

      The app code

      Predict

      Mei installs Docker. She runs your lunchbox on her laptop. What happens?

      Check

      A container fixes the kitchen, not the recipe. Which problems does it fix?

      Drag a card into a box. Or tap the card, then tap the box.

          You did it!

          You can now explain why containers exist.

          Go deeper (optional)

          Containers help whole teams. A new teammate gets the app running in minutes. The server runs the same box you tested.

          Real rep (optional): ask a friend to type node --version. Compare it with yours. Different? Now you know why containers exist.