If you see the above output, then your XNAT VM is set up correctly.
Here are some commonly used commands, or ones that can give you more information. You don't have to do them now, but you may want to return to this page for reference later if you don't remember how to do something.
You can learn more about what commands you can give docker using the built-in Docker help documentation.
xnat@xnat-31:~$ docker help
docker help can also tell you more about each specific command.
xnat@xnat-31:~$ docker help <command>
xnat@xnat-31:~$ docker images
This lists all the images installed on the local docker server (you will have none right now).
xnat@xnat-31:~$ docker ps
This lists the running containers on your docker server. Again, you will have none right now. If you want to see all containers—including ones that haven't started running or have already finished—you can include the -a flag.