Rimworld

Hello,
I started playing the game and it's awesome! However I don't really understand how moving with the colony works. I found out that you can indeed move to other tiles, but it seems like it's impossible to have 2 colonies then that trade with each other, after for e.g. telling half of the population to go and settle somewhere else. It seems like you can always only have one.

In this case what's the point of progressing on one part of the map? In the end resources on that tile of the map are finite. What happens when I for e.g. harvest all stone that exists on my part of the map? How do I continue building? Or if I run out of building space, etc.?

If moving is the goal what's the point here, because as far as I understood it's not really possible to move all stored items etc. to another place, so at the end you always loose what you have build or farmed?

Probably the answer is simple but that's the main point I didn't have figured out about the game yet.