Ebay Returns question?

-Okay so i contacted the seller about returning the items, and she gave me the address to send it to, and said to include the item numbers? I emailed/messaged her all of the item numbers in the first message, so what does she mean? Do i just write them on a piece of paper and put it inside the envelope/box? is there a way to put it on the shipping label? I'm just confused about including the item numbers? I'm new to ebay help!