Curiosity is an unmanned rover, meaning there are no people on it. What is it's scientific mission?

The rover's goals include: investigation of the Martian climate and geology; assessment of whether the selected field site inside Gale Crater has ever offered environmental conditions favorable for microbial life, including investigation of the role of water; and planetary habitability studies in preparation for future human exploration.

Its mission is to search for any life form on mars, also to take samples of the planet so scientists can understand what happened to it.