New Twitter users are often confused about how to send a private message to another user. All of your tweets (posts) are available for anyone to view online as part of your ongoing Twitter stream, but it is possible to send private messages to other Twitter users with the Twitter Direct Message feature.
In order to send a direct message to another Twitter user, that person must be following you. Once the person you want to send a private message to is following you, simply select the Direct Messages link in the righthand sidebar of your Twitter profile (you must be logged into Twitter), and choose the person you want to send the message to from the drop-down menu near the top of your screen. Type your message in the box provided, and hit the Send button. Your direct message will appear in the recipient's Direct Messages Inbox.