Even with our current technology, it would be possible to live on Mars, so long as
we stayed in space-suits or built stations which would maintain temperatures and oxygen levels. We would then have to keep bringing out supplies to keep the astronauts going – food, drinking water and even oxygen. There would be no way of growing food on Mars without oxygen, there is no liquid water on Mars and no oxygen in the atmosphere. This would all cost a LOT of money, and it currently would take several years to fly between Earth and Mars.
The main difficulty with keeping life on Mars more permanently is that there is no
oxygen in the atmosphere, that the temperatures range from -85 to -5 degrees, and that there is no liquid water (there is lots of ice at the Martian polar ice caps). To change this, we would need to build up the thickness of the atmosphere (which is currently far thinner than Earth’s) by pumping in gases
from somewhere. This would increase the thickness of the atmosphere, hopefully warming the planet up enough to melt the ice caps and generate water. I don’t think anyone really knows of a way to do this yet.
Finally, we would have to keep the atmosphere in place. Scientist believe than Mars once had some sort of atmosphere, and that bacterial life might even have been able to survive. However, through time this atmosphere was stripped away. One reason for this is
that Mars does not have a magnetic field like earth. Our magnetic field deflects solar winds away, so they don’t affect our atmosphere. With no magnetic field, Mars has no ’shield’, so
solar winds may well blow the atmosphere away again. We would need to find a way to solve this problem as well, and I’m not sure how we would do this.
I don’t think we will be colonising Mars during our lifetime. However, one day we might
want to. It is estimated that in 7 billion or so years time, the Sun will heat up as
it begins to become a red giant, making the earth uninhabitable. Mars, a little further away and so a little cooler, would then become a potential home, if we could terraform it appropriately. That is, of course, if the human race is still around in 7 billion years, which is extremely unlikely. Hope that answers your question!