How to Do Black Metal Vocals

Listen to black metal and understand what it's about. Secular black metal is about evil, death, and depression. Make the sound you think somebody would make with their last breath if they were slowly dying. Use that sound to form words. However, Christian black metal is about positive/negative topics related to Christian beliefs.

Decide what kind of scream you want to do. Do you want a Marduk "argh I messed up my voice" sound, a Krieg/Burzum "pitched" sound, a Chthonic "Screamed" sound, Malevolentia "Shriek" sound, or the "Sabbath" burp?"

Learn about the different types of voices you can sing in. Singers and vocal stylists use the terms "chest voice" and "head voice" to refer to using different parts of their vocal chords to achieve different effects. For a shout like, Krieg-esque approach, you'll want to practice singing in chest voice quite high, but not breaking into head voice.

Add a raspy like sound to your voice by gurgling slightly at the back of the throat once you can sing comfortably at a "shout" pitch, and push with the diaphragm (try tensing your abdominal muscles). This should produce a quite high, shout like sound if you're doing it right.

Start trying to increase the strength of your "gurgling" technique (slowly - don't push yourself too hard, or you'll ruin your voice), increase your range (once again, slowly, for the same reasons), etc.

Try singing while applying the same technique you learnt in step 2 - the rasp effect, but without the diaphragmatic support, for a different style. Many trainers/teachers will tell you that this is a really bad thing to do, singing without diaphragmatic support, but in some instances - such as in a soprano voice - it can't hurt.