Pokerstars is a company website offering only free play games. The pokerstars domain is used primarily in their TV advertisements since there are no real money games available at this website. This avoids any legal issues or censorship of using their pokerstars domain which allows real money games.
PokerStars is one of the most successful and profitable poker sites the industry has ever seen. Nobody has been able to rival their dominance for over a decade now. And no matter what you think of their new ownership, they continue to crush it in every possible way from a business point of view.