A basic break barrel shotgun has an extractor that connects with the brass rim of the cartridge and pushes it out of the chamber sufficient to grab it with your finger tips and withdraw it from the barrel. That's its only job.
An Ejector, not only connects with the brass rim of the cartridge and pushes it out of the chamber, but in addition, when the cartridge reaches a certain distance out of the barrel, the Ejector takes over and has a light spring mechanism which pops the spent cart right out of the barrel nicely landing a couple of feet away (not yards) so you are free to load another and shoot again in a lot less time, whilst still being in sight of the discarded cartridge to pick it up.
If your a dab hand and not rushing for a second shot, you can break the barrel and catch the cart mid-air.
It will also eject an unspent cart - as its spring assisted, not gas or inertia reliant.
(Also great for gloved fingers, or less abled hands.)
Think that covers it?