Hey, newbie guitarist here (a week or so), so please forgive if this is a retarded question (which it probably is), but I have to ask: what do the musicians do to create that cool squeal in the beginning or end of their songs? I've noticed it in black metal and death metal mostly, and I just think it sounds cool so I am curious as to how it's done. I sometimes do it myself on accident but I am not completely sure what I am doing, haha. Example:

The sound in the beginning here:

That would be feedback. That's done by turning up the guitar while standing near an amp with a shitload of gain.

yea that's just feedback. pretty much what awblaster said. And what kind of feedback you get is completely dependent on what guitars and amps you use.