Hi Kami,
NASA has sent a bunch of robotic spacecraft to Mars looking for life or signs of life in the past. We have determined that there is plenty of water ice there below the surface..which we think is required for life. Another robotic spacecraft, Mars Science Laboratory, will head off to Mars next year. It will use robotic instrument to look for signs of past life from a time when the water was flowing on the surface.
If humans had to live on Mars, they would have to be in spacesuit..or in a structure with an artificial atmosphere. So first NASA would need to build an astronaut base on Mars and figure out just how humans might live there. At least there is water!
Paulett (a NASA scientist)