VirtualBox includes an easy to user shared folder option in the settings. It allows anyone to add a folder from the host computer and share it with the guest. All that is required is for the guest OS, in this case Ubuntu to have the Guest Additions installed. This can be done using the Devices > Install Guest Additions… menu options.
On the guest Ubuntu side the permissions are very restrictive. It only allows root and a new group called vboxsf to access the mount point. For the user to access the shared folder, add the user to the group vboxsf:
sudo usermod -aG vboxsf [username]
where [username] should be replaced with the actual username. For example adding the user danny to the vboxsf group:
sudo usermod -aG vboxsf danny
After running the above it is necessary to log off and log back in for the changes to take place.