Draw in a full and deep breath (see the breathing exercise), sing the tone, "Aaaaah." As you sing the tone, release the breath slowly, first from the belly, then up through the chest. ... Breathe in again, and sound out, "Aaaaah."
Imagine that there is a column of air resting on your belly extending up through your lungs to your throat. When you sing, visualize this column of air coming all the way from your belly, supporting the tone coming out of your mouth. In other words, sing from your belly!
Breathe into your belly and sing. "Aaaah."
Again - "Aaaaah." And again - "Aaaaah."
Singing from the belly gives us more air, the ability to sustain our tone longer, and more control over our voice. We initiate a self-reinforcing cycle: our deep and full breathing helps us to chant, while the elongated and rhythmic phrases of chant entrains our breath, making us one with the music.