The other name for twitter is micro blogging, which is becoming immensely popular as a medium of social networking. The medium is based on letting people know what you are doing. People can remain in touch with one another instantly using the messages, known as tweets. The maximum allowed characters for the message is 140 and hence, you have to convey your message using short text.
Your answer to the question ‘What you are doing’ could be letting the world know about your business, hobbies, emotions, or anything else, that you feel that people would be interested in knowing.