How do you make someone your companion and give them permission to your tardis

I swear... I'm having De'ja vu. Did you post a thread on this before?

[Heh... Talking about De ja vu and it double comments. How ironic]

Here you go.

I didn't post a tread on this before but thank you.

but sometimes De'Ja vu means whel you can let the web explain it.