How come free websites like facebook are worth billion dollars?

[Stabbers]

Is it just through advertising?
but i hardly see any.....
In the television industry, the subscribers pay the DTH companies who in turn pay the distributors and finally the channels get paid.
Is it the same here? Suppose i use facebook for 1 hour, then will facebook be paid for us using it for an hour? If not, then how do they wrap in such huge profits?

[UnVerified]

I'm pretty sure it's mostly advertisements.