First, select the unit that you want to build by clicking on its picture in one of the panels on the right side of the screen. The selected type of unit appears in the large box on the left side of the screen. All civilians cost 3 paper and $500. If you lack the required paper or money a red x will appear. 

Click the right arrow to increase the number you are building, and the left arrow to decrease. The number you have ordered appears in the text box and near the unit picture on the right side of the screen. All units take one turn to build and are available for action next turn. Unlike military and naval units civilian units do not require a peasant for construction, nor do they eat any food.

Note that it is not possible to delegate unit construction to the computer.