It's a tech you have to activate in the research tree. In order to open it, you have to activate the Marble, Steel, and Plank factory techs. The boost will be for one of those goods (ex: Marble Production Boost). Once open, fill with required kp, then activate by paying the resources required. Once activated, you will make more of that good than the other 2. As you collect relics that correspond to that good, the percentage boost goes up for that good, so plan to focus most on building/upgrading those factories and trading for the other 2 goods.