This is hard to explain (as I'm not a vocal teacher) but I'll give it a go. It is something you'll feel for yourself. You need to take a deep full breath 'into your stomach'. This is a proper breath which many people don't do. To breathe in correctly, your stomach should move in and out, and not just the lungs. Many people just use the lungs which is inefficient. You can just use your lungs (poor), just use your stomach (much better) or both together (the best, but harder to acheive). This 'stomach' breath is actually your diaphram 'pulling your lungs down and out thus increasing lung capacity... which pushes your stomack out to make room for the extra lung space. This is also a much more controlled breathing... you can hold your breath longer and control it better... all important things for the singer.
Practice this deep 'stomach' breathing by 'pushing' your breath 'down' into your stomack when you breathe in. You should notice that when you breathe out, pushing again but using your stomach, your breathe is much more powerful and rich. This is the breath to use to carry your voice. Try not to sing a note, but instead try to breathe out in this way and 'push' the note from your stomach.
I'm not sure if I've explained the technique clearly enough, but give it a go. Practice breathing in and out of your tummy, and then try to originate the sounds from there.