why stop container in docker code example

Example 1: stop all container in docker

docker stop $(docker ps -a -q)
docker rm $(docker ps -a -q)

Example 2: stop docker container

//Check if the container is running
docker ps -a

docker container stop {container-id}

Example 3: how to stop docker

systemctl stop docker.service
#(OR)
systemctl stop docker
# it will start docker