Reputation points are the in-game currency.
 
Reputation points
 
They're needed to build a new sawmill and evolve blueprints of the houses in the Workshop.
 
Reputation points for the new sawmillReputation points for blueprints of the houses
 
To start earning them, you need to build the workshop. You can find it to the right of your sawmill.
 
Build the workshop
 
Then you can get reputation points by completing workshop orders for constructing houses.
 
Reputation points for workshop orders