Writing is believed to have originated by the simple drawing of ideograms: for example, a drawing of an apple represents an apple, and a drawing of two legs may represent the concept of walking or standing. From this origin, the symbols become more abstract, eventually evolving into symbols which seem unrelated to the original symbol. For example, the letter N in English is actually from an Egyptian hieroglyph representing the same sound, but depicting waves in water - the Egyptian word for water contains only one consonant /n/, and the picture eventually came to represent not only the idea of water, but the sound /n/ as well.
"Writing" is also often used to describe the craft of creating a larger work of literature. This is an extension of the original meaning, which would include the act of writing longer texts. Calligraphy is the art of beautiful writing.