Just like you may have done at yoga or seen yogis and the likes practice. Chanting different tones vibrate different endocrine glands throughout your body (ancient yogis referred to these areas of glands as Chakras).
If you practice now, you’ll notice that "Aaaahh" vibrates in your lower torso area, "Oooohh" in your heart and throat and "Mmmm" vibrates in your head.
It also vibrates your vagus nerve which is a main component of your parasympathetic nervous system. Chanting even calms down your pain receptors (which is one of the reasons why you yell when you get hurt).
During this meditation you’ll breath in the nose for 4 seconds and then chant Aaaaah, Oooooh, Mmmmmm for 12 seconds.