How Facebook Web likes help?

So, if it helps in the case of SERP. What is the mechanism that G will know about Likes? I guess profile pages where they appear are mainly private.

If the pages are private, I guess, G can not index those in any way?

If you have a website with integrated FB plugins, then the Likes are visible by human as well as the Google.

That makes sense, I had not thought of it that way, thanks

Right now I believe Google has not really integrated G+, FB likes, Tweets to affect SERP's. But it is said that in coming future likes from the social networking will highly affect keyword rankings.

I think it did. And I think it will even more in the future. I am not sure though

I know from some people that google loves sharing on social networks and commenting

I think that will be helpful if you promote a product because it appear that when many are likes on it. Meaning that product is good

Like Bookmarks some time ago it will be part of the algo, but not the holy grail to solve ranking. just another piece of the big picture