How do ailerons control aircraft roll and what is adverse yaw?

Ailerons are hinged surfaces on the outboard trailing edge of wings that deflect differentially to control roll. When the pilot commands roll, one aileron deflects up (reducing lift) while the other deflects down (increasing lift), creating a rolling moment. Adverse yaw occurs because the downward-deflected aileron also increases drag on that wing, causing the aircraft to yaw opposite to the intended turn direction. This is counteracted by rudder input, differential aileron deflection, or Frise ailerons that create drag when deflected upward.