Hey @Janice, this is pretty simple. Create a container
docker create [OPTIONS] IMAGE [COMMAND] [ARG...]
bash into your docker container
docker exec -it <container name> /bin/bash
and then install puppet agent on it.
have a look at this thread on how to install puppet agent on Linux: https://www.edureka.co/community/40887/how-do-i-install-puppet-agent-on-linux