best way I've found to learn it - stand up loosely, feet
shoulder width apart etc, put a hand on your stomach to make sure
you're using it - your shoulders shouldn't move at all, and go up
and down scales but on every note take a deep breath and do a very
over the top 'oh' or 'ah' sound for it and strongly force the air
out without moving your shoulders, so it effectively seems to be
coming from your stomach. you'll probably only manage a few scales
before it starts to ache or hurt a little first time but you'll get
used to it after a while (by that i mean stop and do it again later
not carry on when it hurts) - after a while you'll find it gets
easier and, hopefully, you'll be able to translate that technique
into controlled breathing and singing for your songs 
