Condensed from Twitter -
What is Twitter?
Twitter is an exchange of quick, frequent messages, called "Tweets" of 140 characters or fewer. These messages are posted to your profile, sent to your followers and are searchable on Twitter search. Unregistered users can read tweets, but you must be registered to send as well as read them.
Tweeting - Once you've registered, type your messag or 'tweet' into the box labeled "Compose New Tweet" in the upper, left side of the screen. A counter at the bottom of the box will tell you how many characters you've use. When you hit return or the Tweet button, your tweet will appear in the long list of messages on the page, or your newsfeed.
Following someone means you've chosen to subscribe to his or her Twitter updates. When you follow someone, his or her posts will appear on your Twitter home page.When you create an account, you can search for people by name or user name, import friends from other networks, or invite friends via email. You can also follow people suggested.
Reply, Retweet, Favorite - You can interact with the messages that appear in your newsfeed. To respond to a post, hit reply and type your new message in the box that appears. When your new message appears in the news feed, it will contain an 'expand' link that lets you see the original message as well. Users can have entire conversations like this.
Engagement - A 2013 Twitter study shows customers share positive experiences about businesses they follow on Twitter with their own network of followers (64%), retweet business tweets (70%), and are more likely to repurchase in the future (72%).