Installing Docker & first commands

On Linux, Docker Engine installs directly on the OS. On macOS/Windows, you install Docker Desktop, which quietly runs a small Linux VM behind the scenes — Docker's daemon needs a Linux kernel no matter what desktop OS you're on.

# Ubuntu/Debian — official convenience script
curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh

# run docker without typing sudo every time
sudo usermod -aG docker $USER

# verify it's alive
docker version
docker run hello-world

Three moving parts, every install: the daemon (dockerd, does the actual work), the CLI (docker, what you type), and the REST API the CLI quietly speaks to the daemon over a local socket. You'll basically never touch the API directly, but knowing it's there explains why some GUI tools can control Docker without you typing anything.