You will unlock this by playing the game normally. Set up a colony with water, air and electricity production. After you have set up the necessary resource generation for mars, you will need to build a dome, first buildings for housing and a grocer or diner. After this has all been set up its time to launch a rocket with citizens to populate Mars.
To get a rocket with passengers press
scroll to Resupply and press
. Select passenger rocket. Press
to review your applicants (you may also filter out perks flaws age and other things in here) and select at least 1 to send to Mars. Press
to launch and they will be on the way to Mars. The rocket also includes 10 food per citizen so food should not be an issue.
It will take some time to get the rocket to Mars with your new colonists so you can fast forward until the rocket is ready to land. Select a landing spot and the colonists will disembark and move in. Now you will need to keep them alive and wait for 10 Sols to pass in order to pass the approval stage. Make sure water, electricity, oxygen, and food are all sufficient. It will give you an in-game notification if some of your citizens are in need of something.