Twitter is a social media platform that allows users to share messages called Tweets. Tweets can include text, photos, videos and links, but are limited to 140 characters. Users create a profile with a username and can follow other accounts to see their Tweets. Features include liking, replying to and retweeting other users' posts, as well as sending direct messages. The guide outlines best practices for using Twitter safely, such as using privacy settings and avoiding sharing personal information.