Pour sortir de la machine virtuelle : Touche "Diamant" (Ctrl en bas à droite sur mon clavier)
Display : http://askubuntu.com/a/455140
Independently of your installed version of VirtualBox you should install the latest version of the VirtualBox Guest Additions into your Ubuntu-Guest. You can get it from the Ubuntu-Software-Repository.
Startup your guest and hit Ctrl+Alt+T to open a terminal session. Type
sudo apt-get install virtualbox-guest-dkms
to install the latest package. Restart the VM and enjoy screen-size.