Screamo

Can some one please give me some tips on how to scream/growl correctly? Like whenever I try to I cant seem to get the right sound. And from all the videos they say "use you diaphragm" and I just can't seem to get it right. I can breathe using my diaphragm, but other than that I'm like completely confused on how to get my growl/scream just right. Like I'm completely lost on how to get my voice that way. So if someone could please give me some good and helpful tips on how to scream/growl it would be greatly appreciated! :D