Building a Settler: A city that builds a settler loses two citizens from its population. Founding Cities: Settlers are used primarily to found new cities. Move the settler to the desired city site, and, when the settler is active in that square, press B. Joining a City: A settler may also be used to increase the population of an existing city; when the settler is active on a city, click the "Join City" button. The settler disappears and the city's population gains two citizens.