In essence, all art represents a reality or thing that the art itself is not. But in terms of style, abstract and representational artworks are easy to differentiate between.
Representational artwork appears to be very similar to a real subject, while abstract artwork does not look like anything found in reality. Instead, it uses conceptual ideas to reflect things or images.
The symbol of a woman on a canvas is representational, because it is easy to recognize the figure and what she represents. But the symbol of a red cube on a black background is abstract, because its purpose and meaning are not clear.
A representational painting could be something such as a still life of a bowl of fruit, while an abstract painting of the same theme may only feature geometric shapes.
Music is almost entirely abstract, because there are rarely cases in which it represents something real. Exceptions exist, such as when music intentionally sounds like nature (mimicking bird tweets or pouring water to reproduce rivers, for instance).
In general, representational writing is usually seen as prose, while abstract writing typically is employed in poetry.