The meaning of this poem is that after dark, birds know how to fly to the woods to roost, and floating clouds will float behind the mountains to wait for their return the next day.
The sentence "Tired birds return to the woods at dusk, and floating clouds return to the mountains in clear skies" comes from Bai Juyi's poem "Farewell to Yang Yingshi Lu Rou Yin Yao Fan". This sentence is often used to express that people should return to their destination, or end a busy day and return to a peaceful and peaceful life.
The tired bird and floating clouds both symbolize that people should return to their homes or spiritual destinations to enjoy peace and comfort after being busy outside.