A free site does not cost the surfer anything to view it. The idea is that while the surfer is looking around the pages of a free site the webmaster gets them to choose a link to a paysite which they will get credit for upon the surfer joining. Free sites come in many different shapes and sizes and there really are no rules. A standard free site would have a warning / home page, then a full page ad, and then a number of galleries. Although it's worth mentioning that 'no-content' sites can also be made - where there are ONLY adverts shown on the various pages.