This will be your first achievement and will pop during level 9 (unmissable). This level is very food dependent, so make sure to get that upgraded quickly. I did not upgrade the sawmill or the blacksmith. Once the portals are built, the worker will run back and forth between the energy generator and the portals to power them on. Kind of like the fireman in the other games, so make sure to give yourself a little cushion in time. Other than that, it is pretty straightforward. I didn't get 3 stars the first play, but that was because I didn't get enough food generated for the end.