You mean the shouty vocals typical of thrash? It's basically just shouting.
If you mean the fry screams common in some melodeath (like ATG), you do them on the vocal fry.
If you mean the gutturals typical of stuff like Cannibal Corpse, they're on the false vocal cords.
_________________
The Party told you to reject the evidence of your eyes and ears. It was their final, most essential command.
If you're not careful, the newspapers will have you hating the people who are being oppressed, and loving the people who are doing the oppressing. —Malcolm X
Real power is achieved when the ruling class controls the material essentials of life, granting and withholding them from the masses as if they were privileges.—George Orwell