In VirtualBox, go to Devices -> Shared Folders.
Add a shared folder and call it shared_source.
Go to a folder (in the guest OS) and create another folder called shared_target.
$ sudo mount -t vboxsf -o uid=1000,gid=1000 shared_source shared_target
where the uid and gid are the user/group ownership you want for the mounted files.
Networking - Shell