1. First you will need to have both the Assassin's Creed III: Liberation game cartridge for the PS Vita, and the Assassin's Creed III game disc for the PS3.
2. Make sure that you have AC3 saved data already available on the PS3.
3. You will need to launch the PS3 version Assassin's Creed III, go to the Extras menu and choose the Connect a PlayStation Vita System selection.
4. Now start the PS Vita, launch Assassin's Creed III: Liberations and go to the Extras menu and choose the Connect a PlayStation 3 System selection.
5. You will then see the notification that the content has been unlocked.