Your Peons/Peasants are not just resource gatherers; they are also your builders. Select a worker, then click the 'Build' button to bring up the construction menu. Buildings unlock new unit types and research upgrades. For example, a Barracks allows you to train Footmen/Grunts. Always plan your base layout to be defensible and efficient. Prioritize building structures that unlock essential units or upgrades for your current mission objectives.
