You are only allowed to ask one question. Multiple questions are not permitted, so I have had to edit your question to focus on the exposition of this great short story. When we think about the plot of a story, the exposition of the plot is the opening of the story, when the characters and their conflict are introduced. It is also known as the basic situation.
Therefore, when we think of the exposition of "The Monkey's Paw," we can see that it is the beginning of the story, when we are introduced to the Whites and their mysterious guest, Sergeant Major Morris, and also the monkey's paw, which we are not sure whether to take seriously or not. Note that Herbert White and his father seem rather dismissive of the paw at first, but their scepticism is halted somewhat by the obvious fear that that Sergeant Major Morris expresses towards the paw:
The soldier regarded him in the way that middle age is wont to regard presumptuous youth. "I have," he said, quietly, and his blotchy face whitened.
Of course, the rising action begins as Mr. White makes a wish on the paw and the chaos that ensues is unleashed.