How do the people who manage sites like Google or Facebook get paid?

[the kid with the questions]

I mean, they're free to use, but definitely require people to update them, etc. But, if they're provided to anyone with access to the internet, free of cost, then where does the income come from, to pay the people who keep the sites functioning? I know there are advertisements on both sites, but surely ads can't be their sole source of income, right?

[rafyas2002]

As you yourself mentioned, Ads are a source of income and a good source. Beside Ads, users give very important information to such websites, for example the managers of facebook know the interests of their users so they can use these information in many ways such as Intelligent advertisements or google can prepare precious polls just by checking the frequency of use of a word or a phrase in the search field. They can feed even some governments by letting them know their people's interest or the way the people react in a specific situation.