The oil drain plug on a car is located at the bottom of the oil pan, which is located at the bottom of the engine, states the Dummies website. Vehicle-specific schematics are available in the vehicle's owner's manual.
The oil drain plug is a long bolt that is screwed into the bottom of the oil pan, according to the Pennzoil website. Some vehicles are equipped with two different drain plugs, which allow the oil to drain faster. Vehicle owners can change their own oil by removing the oil dipstick, placing a pan under the oil pan and removing the drain plug to drain the oil. Follow all safety precautions and instructions outlined in the vehicle's owner's manual.