Colonies

Colony Building is a feature that will be in Kerbal Space Program 2. The way colonies will be built is from resource gathering. Once enough resources are gathered, the colony can be created and start being expanded upon. Once a colony reaches a certain level of advancement, it becomes a place where vehicles and ships can be constructed, similar to the Vehicle Assembly Building back on Kerbin. From what we know, it seems the importance of colonies are to eventually build interstellar ships on airless bodies like The Mun and other locations, making it much easier to launch them compared to building and launching one from kerbin in the VAB, since due to Kerbin's atmosphere, it would be harder to keep the craft from getting destroyed during launch.

Description
From the game's steam page, the description about colonies reads:

"Brand new to Kerbal Space Program 2 are colonies.. These colonies not only pose their own physics challenges, but also require resource gathering to build structures, space stations, habitations, and unique fuel types. Eventually, these colonies become advanced enough for vehicle construction, propelling deep space and beyond."

More Info About Colonies, From A KSP Loading Article, Reads: "Long term colonization of celestial bodies has become a priority for Kerbalkind. Gather resources to construct buildings, space stations, and habitations, as well as find and process unique fuel types. Eventually, these colonies become advanced enough for vehicle construction, propelling them towards deep space and beyond. It’s time for Kerbals to become a type 2 civilization!"

O2 and food
After you build your colony you might worry about you kerbals might die from lack of food (yes you'll need food) or lack of oxygen (need that too) DON'T WORRY!!! if you run out of lets say food your kerbals will become terribly inefficient but they wont die.

Kerbals in uhhhh in their private time....
Kerbals can have Kerbal kids on your colonies when you build a nursery making new disposable test subj.... I mean Kerbalnauts.

We unite
after you build colonies on lets say Minmus and one has little food and the other has a lot then you don't want to make a supply ship and fly across, do you? FEAR NOT!! as you can make "trade routes" where they can share resources.