“Air spinning” is the projection and expelling of the air through the nose. Notice the two positions in fig. 6/6A: rest position and yawning position, already explained above (attack on the breath). The arrow indicates the air pathway, that has to be free from constriction and continuous for the whole phrase or vocalize.
When you start to sing you have to project the sound and the air outside and forward, imagining the sound separate from the throat.
In fact, if you let the voice follow the air spinning (Fig.6A) you will hear a heavier sound, because you will listen it with the inner ear. On the contrary, if you project the sound outside you will hear your voice lighter, because you will listen it with the outer ear. This doesn’t mean that the voice will be less strong, indeed it will be more rich in harmonics.
You can experience inner and outer listening sensations: closing both ears you will hear the inner sound, alternatively opening the right and the left one you will locate the external sound.