In a nutshell, Blingo preselects certain times of day when a prize will be given away. If you execute the first search after that time, you win the prize. Only your first ten searches each day are applicable, so you're not really doing yourself any favors by sitting at the keyboard and executing search after search.
And the searches are actually carried out by Google, so you know what the results will be like. PCH funds the prizes given out thru Blingo from part of the revenue they get from the Google search ads. (Now if I tried to get people to run extra searches that way, Google would say I was running afoul of their TOS!)
Anyway, check it out. Sign up thru my links, and have fun. (Disclosure: If you win something after signing up thru my links, I'll win it, too!)