At some stage of the mod Earth will meet the Vulcans and forge an alliance. When this occurs will depend if you play the map that will be included with the mod where Vulcan is close to Earth or play a random map where Vulcan could be anywhere if at all on the map.
If you play a random map it is recommended during setup of the game that the Vulcans are one of the races that will appear on the map.
When Earth and Vulcan become allies then Role Play will eventually follow the steps where Spock has gone through Starfleet Academy and has been assigned to the Enterprise.
When this happens the Enterprise will head to Earth and pick up Spock.