Mouting the shared folders in ubuntu guest

To mount the shared folder in the guest, just run the command bellow with the name used while creating the shared folder.

sharename="whatever.you.want.to.call.it"; 
sudo mkdir /mnt/$sharename
sudo chmod 777 /mnt/$sharename
sudo mount -t vboxsf -o uid=1000,gid=1000 $sharename /mnt/$sharename
ln -s /mnt/$sharename $HOME/Desktop/$sharename

Installing VirtualBox Guest Additions

1. Login as ubuntu;
2. Update your APT database with sudo apt-get update, and typing your password, if requested;
3. Install the latest security updates with sudo apt-get upgrade;
4. Install required packages with sudo apt-get install build-essential module-assistant;
5. Configure your system for building kernel modules by running sudo m-a prepare;
6. Click on Install Guest Additions… from the Devices menu, then choose to browse the content of the CD when requested;
7. Mount the cdrom with "mount /dev/cdrom /media/cdrom";
8. Run sudo ./media/cdrom/VBoxLinuxAdditions.run, and follow the instructions on screen.