Theres not much to screenshot... it is literally a single task (with the variable set up inside it) followed directly by an expression robot with the above code placed in it.
By setting the variable in the task via the workflow administration utility, it makes the field visable and editable to the user when they recieve their task. They enter in a value and complete their task. The flow then goes from the task to the aforementioned expression robot. The robot grabs the value that the user entered and stores it in the attribute so that the value now shows up on the details page of the change object.