To remove all containers,
docker rm -vf $(docker ps -a -q)
-v: Remove all associated volumes
-f: Forces the removal. Like, if any containers is running, you need -f to remove them.
To remove all images,
docker rmi -f $(docker images -a -q)
-a: for all containers, even not running, (or images)
-q: to remove all the details other than the ID of containers (or images)