Mars is a rather harsh environment when it comes to human habitation. For one thing Mars has essentially no free diatomic oxygen in its atmosphere. Hence a human could live for 2 or 3 minutes in the Mars atmosphere. After that, human would die.

Secondly, it is VERY cold on the Mars surface; the average temperature of Earth is about 50 degrees Fahrenheit; the average temperature on Mars is - 100 degrees Fahrenheit (below zero)!!!! Cold!!!!!!

So unprotected, a human would die of freezing and lack of oxygen on Mars. However, a human could persist in a protected environment in a heated capsule with source of oxygen.

Yes and No. As Mars is right now humans could not live there without a space suit. The air around Mars is not breathable by humans and the gravity is much less than on Earth. Humans might have long term damage to bones and muscles similar to that suffered by someone who lives on the space station for a long time. The is also no significant atmosphere to protect humans from the sun’s radiation.

At present time, no - the air on Mars is thin enough that a human's blood would boil if he were on the Martian surface without a space suit. As far as future colonization and technology is concerned, however, Mars would probably be the most easily colonized planet in the solar system after Earth.

No, humans cannot live regularly on Mars as they do on Earth for various reasons. One is temperature; the temperature of Mars on long polar nights hits -180 F which is way too cold for any human to survive. Another reason is that there is a thin layer protecting Mars which means more carbon dioxide and less oxygen levels, and also it is protected against radiation. Humans need enough oxygen to live and need protection against radiation to be healthy and not get cancer. The third major reason is that the atmospheric pressure is not suitable for humans just like how when you go deep in the ocean the pressure increases.

Humans can live on Mars, but only with specialized equipment. Because there is no air to breathe on Mars (there is an atmosphere, but there's too little oxygen), we need to produce our own. Also, the average temperature is -63 degrees Celsius (-82 F), so we need insulating suits and habitats to protect us from the cold. These are only some of the challenges we face trying to live on Mars. However, there is currently a mission planned by a private company to send humans to permanently live on Mars by 2023! Time will tell if they're successful.