A man wearing dark knee boots, a green cape, and a hat with two big feathers on the front is sitting by himself on a bench in front of a building with a blue and white patterned piece of wheeled luggage to his right while he rests both his hands on a walking stick.
A man with a walking stick sits by himself.
A man with a walking stick sits is part of his overall description wearing dark knee boots.
"A man with a walking stick sits by himself" is another way of saying a man sitting by himself with his hands on a walking stick.
The man is with a walking stick because he rests his hands on a walking stick.