You stand on the bridge and look at the scenery, and the people watching the scenery are looking at you upstairs. The bright moon decorates your windows, and you decorate other people's dreams.
The third sentence "The bright moon decorates your window" actually refers to the fact that what you see through the window when looking at the scenery is you, and if you look back at the scenery, this is your window. , you look at the scenery through the window. This window allows people looking at the scenery to see you. This window plays the role of allowing others to see you. This window is made for others to see you, so it is also your window. This is where the third sentence comes from.
So you are watching the scenery on the bridge, and the people watching the scenery are watching you through the windows upstairs. The bright moon has decorated this window that belongs to you, and you have decorated the dreams of the people watching you.
This poem is overly narcissistic, and "your window" is also quite overbearing. It's just that the author loves to look at a person, so how does he know that the person looking at the scenery is looking at "you".
The last two sentences are actually false sentences. The real artistic conception is:
You stand on the bridge and look at the scenery. The people watching the scenery are looking at you upstairs. I stand at the end of the bridge and look at you. People who look at the scenery watch you look at the scenery.
The above understanding may be wrong. Another understanding is:
You stand on the bridge and look at the scenery, I stand on the stairs and look at you, and the bright moon decorates your heart. Window, you make me think about it day and night.