How do holding patterns work?
Generally speaking the Flight Management Computer supports holding patterns. The pilot inputs the holding fix (usually a NDB/VOR), the direction of the hold (Left/Right), the inbound course, and the time/distance that one holding leg shall take to execute. These information can be found on aeronautical charts, as IFR holding patterns are published for each airport. As far as I know pilots are also trained to fly holding patterns manually, but you can understand that flying the pattern manually is not as precise as flying the pattern via the autopilot.