What one does is find a zoomed-in image on Google Maps, create hints on how to find it (i.e. in a Slavic country, capital building of President so-and-so), and then post it to the website. Anyone can try it out but there is also an option to e-mail friends the quiz.
According to Martin there are 6,638 different quizzes stored, 108274 quizzes were solved and 927,275 opened. The language of the users seems divided between English and German so some may be hard to solve but try out the English ones anyways.
For the first quiz try to see where Catholicgauze was Fourth of July weekend!