How do familiars work (tabletop)

Currently getting into Warhammer 40k tabletop on tabletop simulator. I've been creating a bunch of different armies and genestealers are one of them. I noticed some of the characters have abilities that mention familiars. Creating my army via force org I noticed that some models have little guys labled familiars.

What I want to know is if familiar models are required to activate abilities and if they are do they require any extra points? Newrecruit doesn't seem to allow familiars to be implemented into army creation.

A quick google search told me absolutely nothing, but the AI mentioned that they cost points. Knowing how untrustworthy the AI is, and the fact that nobody else is talking about it I thought I would ask here.

Thanks!