I just bought Earth 2140 cause the promotion. and I have a problem. I started the game and the second mission in america I can't build nothing! I reed the Walkthrough, but it doesn't help. I simply can't send a Silver One into the builder. Either can't see nothing buildable on the HUD.
I have no idea now if America is the first campaign but it sounds like that. On that mission 2, you have to unpack the prod center from the MCU vehicle in the middle of the map. To do that, select the vehicle, find a suitable place (just drive a bit upwards) and left-click on it so it converts to a prod center. Now you can build more buildings via the HUD. Also see manual page 25.
I have a screenshot attached. When your cursor looks like this, just left-click to create your prod center.