Umm.. rain perhaps, rhymes with pain
You didn’t put the story so I can’t answer the question
I used to have a teacher who said this as well. The best way to understand would be to show examples of how to specify such terms as “stuff” and “things”. For instance: “The birds have lots of stuff.” That was not clear because the reader does not know what the “stuff” is. Instead, the text could be changed to: “The birds have lots of feathers.” Now the reader knows what the stuff is because it has been replaced with a more specific word. If you go over multiple examples in your head, it will become easier to comprehend and you will get used to doing it.
