Twitter is a social media platform that allows users to post short messages called tweets that are limited to 140 characters. Users can follow other accounts and have their own tweets viewed by their followers. It has grown popular for allowing real-time communication, organizing communities through hashtags, allowing users to interact with public figures, and driving traffic to other websites through embedded links. The basics of using Twitter involve signing up for an account, following other accounts, posting tweets from the home page, and including shortened links if a tweet exceeds the character limit.