1. device sharefolder -> set your folder path in windows and set folder name
2. ubuntu terminal:
   1. sudo mount -t vboxsf FOLDERNAME /PATH/OF/FOLDER

For example: 

Windows: share folder: name: share, path: c:???

Ubuntu: sudo mount -t vbox share home/ying/share

enable clipboard share:

sudo apt-get install virtualbox-guest-dkms

set the right to the share_folder

sudo adduser xxxxxxx vboxsf (XXX: your user name)