Take your gun apart (as shown in the manual) and you'll probably be able to figure it out.
The barrel and slide are locked together when the gun is 'in battery' (means cocked with a cartridge in the chamber and ready to fire). When the gun is fired, recoil moves the slide/barrel unit backwards. After a short amount of travel, the cam on the underside of the barrel (take it apart and you'll see what I'm referring to) engages the post on the takedown lever, causing the barrel to drop slightly. When the barrel drops, the slide can continue moving backwards (over the top of the dropped down barrel), eject the spent shell, and then the recoil spring will force the slide forward to reload and recock the gun.
Hard to explain but, as I said, take the gun apart and you should be able to figure out what is going on.