how exactly do the iowa caucuses work?

I know the Iowa caucus is different from a primary in that everyone stands in a big room and people go to different corners to show support for different candidates. But how are the votes counted? Does winner take all and does the whole room’s votes go to the candidate with the majority? Or is it the candidate who has a plurality? Or are all the votes equally counted and reported, as long as a candidate gets more than a certain percentage? Is anyone out there from Iowa and have you attended a caucus in person?