Installing and your first container

In plain English

An image is a read-only package that holds an application and everything it needs to run, such as a base operating system, libraries and your code. A container is a running copy of an image with its own writable layer added on top, so many containers can start from one image without changing it. docker run starts a container from an image, downloading the image automatically from a registry if it is not on your machine yet. The -p flag maps a port inside the container to a port on your host, so a web server inside the container is reachable from your browser. Interactive mode with -it attaches your terminal to the container, while detached mode with -d runs it in the background, and docker ps lists your running containers.

Step by step

1. 1Install Docker Desktop or Docker Engine and confirm it works with docker --version.
2. 2Run a first container with docker run hello-world and watch Docker pull the image.
3. 3Start a detached web server with docker run -d -p 8080:80 nginx:alpine.
4. 4Confirm it is up with docker ps and open localhost:8080 in a browser.
5. 5Enter a container interactively with docker run -it --rm node:22-alpine sh.

docker run hello-world
docker run --rm -p 8080:80 nginx:alpine
docker run -it --rm node:22-alpine sh
docker run -d --name web -p 3000:3000 my-app:1.0
docker ps

Common mistakes

• Leaving out -p means the service listens only inside the container and you cannot reach it from your host.
• Running an interactive container without -it leaves you with no terminal to type into.
• Forgetting -d keeps your terminal attached to the container instead of returning to your prompt.
• Assuming docker ps shows stopped containers is wrong; it lists running ones unless you add -a.