Relax?

Many people translate sung/song to mean 'relax' but this does not adequately capture the nature of this neigong.
Sung feels like the limbs are moving by themselves; all doing is gone.

It is a composite skill which relies strongly upon yielding.
Sung requires the body to be naturally sunk at all times and for the joints to open & close without conscious effort.
Peng permeates the body constantly, creating elastic bow tension although no conscious will is required to manifest or sustain it.
Resistance to force should feel anatomically uncomfortable.
The waist should return to the centre by itself once rotated and the elbows should be heavy.
Sung is not flaccid or inert - it is a cat-like readiness within the mobile structure.

You will not master sung until much later in the curriculum, but you can begin cultivating it immediately.