about Twitter

Twitter has been compared to a web-based Internet Relay Chat (IRC) client.
Tweets are publicly visible by default; however, senders can restrict message delivery to just their followers. Users can tweet via the Twitter website, compatible external applications (such as for smartphones), or by Short Message Service (SMS) available in certain countriesWhile the service is free, accessing it through SMS may incur phone service provider fees.
Users may subscribe to other users' tweets – this is known as following and subscribers are known as followersor tweeps (Twitter + peeps).
Twitter allows users the ability to update their profile by using their mobile phone either by text messaging or by apps released for certain smartphones / tablets
In a 2009 Time essay, technology author Steven Johnson described the basic mechanics of Twitter as "remarkably simple":

As a social network, Twitter revolves around the principle of followers. When you choose to follow another Twitter user, that user's tweets appear in reverse chronological order on your main Twitter page. If you follow 20 people, you'll see a mix of tweets scrolling down the page: breakfast-cereal updates, interesting new links, music recommendations, even musings on the future of education.

In June 2008, Twitter launched a verification program, allowing celebrities to get their accounts verified Originally intended to help users verify which celebrity accounts were created by the celebrities themselves (and therefore are not fake), they have since been used to verify accounts of businesses and accounts for public figures who may not actually tweet but still wish to maintain control over the account that bears their name - for example, the Dalai Lama. Verified accounts can identified by a white check in a blue background, known as a verification badge, next to the user's full name, on the profile itself or next to the name in search results.

Messages

Users can group posts together by topic or type by use of hashtags – words or phrases prefixed with a "#" sign. Similarly, the "@" sign followed by a  is used for mentioning or replying to other users.To repost a message from another Twitter user, and share it with one's own followers, the retweet function is symbolized by "RT" in the message.
In late 2009, the "Twitter Lists" feature was added, making it possible for users to follow (as well as mention and reply to) ad-hoc lists of authors instead of individual authors.
Through SMS, users can communicate with Twitter through five gateway numbers: short codes for the United States, Canada, India, New Zealand, and an Isle of Man-based number for international use. There is also a short code in the United Kingdom which is only accessible to those on the Vodafone, O2 and Orange networks. In India, since Twitter only supports tweets from Bharti Airtel, an alternative platform called smsTweet was set up by a user to work on all networks.A similar platform called GladlyCast exists for mobile phone users in Singapore, Malaysia and the Philippines.
The messages were initially set to 140-character limit for compatibility with SMS messaging, introducing the shorthand notation and slang commonly used in SMS messages. The 140-character limit has also increased the usage of URL shortening services such as bit.ly, goo.gl, and tr.im, and content-hosting services, such as Twitpic, memozu.com and NotePub to accommodate multimedia content and text longer than 140 characters. Twitter uses bit.ly for automatic shortening of all URLs posted on its website.