安靜

In a sentence

• 房间里很安静，只有时钟的滴答声。

  The room is very quiet, with only the ticking of the clock.

  Here, "安静" is an adjective describing the state of the room.

• 请你们保持安静，不要吵闹。

  Please stay quiet and do not make noise.

  In this sentence, "安静" is used as a command asking for silence, functioning as a noun.

• 安静地坐下，我们开始上课了。

  Sit quietly, we are starting the class.

  Here, "安静" is used as an adverb modifying the verb "坐下" (sit down).