This is an interesting thing to do 
It is called "Screaming your guitar"

What you do is you bend the string you want to (It
works best if you use the strings HIGH E, B, G AND D)
because if you use the lower strings it really won't 
scream.

bend one of those strings and barely touch the string
with part of your hand
don't touch the string to hard or it will just mute the 
string
If you touch it lightly enough but hard enough that
you are actually touching the string it will make 
kind of a high pitched scream
It really isn't as bad as an actual scream
It works in a bunch of solo's and a lot of artists
do it.

I think it sounds cool. 

Also Truthfully you can scream it without bending the strings but it's a little easier if you bend it. 

Also works better with overdrive