Cleaning with rags

Paula has asked me to do a post on rags, which, of course, I'm happy to do. This is her request:"I would LOVE if you would do a post on rags. And a pattern for the adorable rag bag you made. What are rags (please don't laugh)? What do you use them for? How many do you need? Are they the same as kitchen towels (I use these as fabric "paper" towels)? Thanks for your blog. I am learning so much."