If you are using virtual box, you may need to easily transfer files with the host operating system. This can be done through shared folder in Virtual Box setting.
However you may not have permissions inside Ubuntu machine to access this folder, you may get an error or be prompted for password.
You can add permission to your Ubuntu user account to access this folder by adding it to vboxsf group to which this folder belongs (replace xxx with your username):
sudo adduser xxx vboxsf
Now reboot. The above command adds user xxx to the group vboxsf. Next time you log on to the Ubuntu, you should be able to access shared folder easily.
To check that the above command was successful use:
groups xxx
You should see vboxsf in the list of the groups that user name xxx belongs to.
OORBS Notes 