The letters m and n represent nasal consonants, the first is bilabial and the second, alveolar.
The sounds for m and n are:
m: man, milk, mother.
n: name, nine, noodles.
M and n are nasal consonants, therefore, the nose need is directly related with the pronunciation of these consonants, since the stream of air is sent through that point.
The letter m is bilabial, therefore, it needs to maintain the lips closed blocking the release of air through the mouth, so the airflow needs to pass thorugh the nasal cavities.
- m is voiced, vocal cords vibrate to produce the sound;
The letter n is alveolar, therfore, it places the interior part of the tongue touching the upper teeth and alveoli of the mouth. In this way, the release of air is also obstructed so the air has to pass through the nosal cavities.
- n: is also voiced, so vocal cords vibrate to produce the sound.
External link to Letters: M, N exercises (1164).