The sentence describing Mulan's hard fighting life in the frontier fortress barracks in Mulan Poetry is

The breath of the new moon is golden, and the cold light is iron.

High school Chinese analysis or fill in the blanks is enough.

Shuoqi

The ancient northern land, also known as the new moon and the old moon, is understood as the cold in the north and the sound of military fighting.

The next sentence is easy to understand, which means that in the barracks of the frontier fortress, the extremely cold weather and wearing metal armor keep you awake at night.