How to Reply to a Tweet on Twitter
When replying to a tweet you are basically getting the attention of a particular user to engage in conversation with. A Reply is a response to another user’s tweet that begins with the @ sign proceeded by the username of the person you are replying to.
Written Tutorial
You can reply to a specific tweet by clicking on the ‘Reply’ icon immediately below a tweet. Twitter begins the reply with the @USERNAME and you just have to type your message after that.
Click ‘Tweet’!
That user will now receive a notification that one of their Tweets have received a Reply.