If you installed with the Docker installer, the NRP is actually not installed in your normal ubuntu filesystem, but in a docker container (kind of a virtual machine).
You can access the docker container with
This will open a terminal inside the docker container and from here you can cd to $HBP and run the baseball_tutorial (you might have to install jupyter notebook with
sudo pip install jupyter
To copy files to your container, you have to use scp commands from your ubuntu, The container IP address can be retrieved with ifconfig from within the container.