Remove the firing pin block. You can just shake it out, or if its kinda stuck from carbon, big tweezers help.

This part is small and easily lost. Be careful, you lose it, your weapon wont fire.

This is the extractor. It pulls out your spent cases (and tosses them in your buddy's face if they stand too close when shooting lol)

If the weapon is fairly new, or gummed up, use a punce to coax it out by tapping it to the rear. Otherwise, you may be able to just push it out with your finger.