Although people may visit mars and enclosures might be build allowing a few scientists to stay on and explore mars for a few months or maybe several years, people can never live on mars. Mars is colder than the antarctic, dryer than the Sahara desert, no oxygen to breath, and almost no atmosphere.
Therefore,if humans are ever going to live places other than on earth, it is be necessary to travel at about one-tenth the speed of light. Otherwise, travel to the stars will take too long.
If it has carbon dioxide, it has oxygen as O2 is what CO2 is made of. Temps can be handled if there's sufficient energy sources. I'd expect bases on the moon or other planets to be underground as it aids in sheltering from solar radiation and add free strength due to pressure differences.
The biggest impediment to a permanent Mars presence is it's weak gravity. That will cause havoc on the human body over time. I suppose the space station has expanded our knowledge about that, but in spite of daily exercise, astronauts suffer bone loss due to the lack of gravity.
Yes, we're obviously a long way from terraforming tech that could let us make other planets habitable. Although here on earth, we have already started terraforming the earth by eating too much meat and driving SUVs.