From the preview:
Recruiting a Companion
If you have an empty Companion space on your TARDIS Console, you may recruit a Companion at the start of your adventure.
If you are on Earth draw from the Earth Companion deck. If not, then draw from the Alien Companion deck. If you are on a Time Anomaly, you may recruit a Companion from either deck.
The newly recruited Companion card is a Part-Time Companion, and will only become a Full-Time Companion if you succeed in the Adventure. Show this by leaving a gap between the Companion card and the TARDIS Console.
Linked Companions
If you have a Link to a Companion, you may search the Companion deck for that Companion to recruit, instead of drawing one at random.
Source