An image is a read-only template. A container is a running (or stopped) instance of it.
docker pull nginx:1.18 # download an image
docker run -d --name web -p 8080:80 nginx:1.18
docker ps # running containers (-a for all)
docker logs -f web
docker exec -it web sh # a shell inside the container
docker stop web && docker rm web
docker images
docker rmi nginx:1.18
docker system df # disk used by images and containers-p 8080:80 maps host port 8080 to container port 80. Always pin a tag such as nginx:1.18 rather than relying on latest, which changes over time and makes builds hard to repeat.
Containers are disposable: anything written inside is lost when the container is removed. Persistent data goes in volumes, which a later post covers.