They can in biodomes those are buildings with plantations of plants who produce crazy amounts of oxygen and in those buildings is everything the same as earth except the view outside

If I was mars I would not want people on my planet getting there dirty feet on me. I only allow aliens there are my friends.

There's so many reasons why we can't live outside earth
other than the obvious lack of oxygen, water, food, shelter from radioactive stuff, and transport.

There are also diseases we could possibly take due to the lack of gravity, mainly to our skeletal system. Just like what happened to Armstrong and his crew... and mostly every astronaut that went out to space.

Also, there was a so-called second earth planet, but it was a long way. takes 2000 years to get to or so...

In the year I think 2027 either the us or Canada are doing a one way muffin they send a man and they don't have enough funds to bring him back so he stayed in a dome with food and oxygen until he dies (this is to see if we could have a small escape planit in times of great distress

It is theoretically possible to create an environment on Mars where we can live safely. However the questions we should be asking are probably as follows:
Is it practical? Nope. Not at all with the millions of dollars we'd need to put into it.
Is it possible anytime soon (at an affordable price)? Probably not

life as we know it might possibly be supported there

^supported, no used to support? yes
Life as we know it can't be supported there currently due to atmospheric differences