What are carriage return, linefeed, and form feed?

Those are non-printing characters, relating to the concept of "new line". \n is linefeed. \r is carriage return. On different platforms they have different meanings, relative to a valid new line. In windows, a new line is \r\n. In linux, \n. In mac, \r.

In practice, you put them in any string, and it will have effect on the print-out of the string.