You donate by contributing content to their sites. How (or if) they monetize this is up to them. As a user, I feel obliged to help others out and I make an ext

You donate by contributing content to their sites. How (or if) they monetize this is up to them. As a user, I feel obliged to help others out and I make an extra effort to answer some questions when I ask one, or when I find a particularly useful answer that helps me with anything work related. This adds value to the site and again, how they monetize is up to them.