The FAL is an automatic rifle, and operates by means of a gas-operated action. The gas system is driven by a short-stroke piston, and the locking mechanism is what is known as a tilting breech block, as to lock, it hinges down into a solid shoulder of metal in the receiver. Magazine capacity ranges from 5-30, with most magazines being 20 rounds.
More information, including pictures: http://world.guns.ru/assault/as24f-e.htm