First, sign up for a free Twitter account at http://www.twitter.com/. When you have logged in, you'll be on the Home page of your account.
On the right side, above the search bar, you'll see the following links:
Home is where you can send messages out to everyone in Twitterville (or the Twitterverse). You can also send a public message to a specific person by putting @their username anywhere in the message.
@your username shows you all replies to your own posts. You'll want to check every now and then and reply back. To reply, hover over person's message and you'll see a star (to make favorite) and an arrow (reply back).
Direct Messages shows you who you sent private messages to and who sent you private messages. To send DM, click on top drop-down arrow for list. Sometimes DMs don't work, and you have to be following that person and they have to be following you to send a DM.
Twitter is an awesome little social network, a tool that anyone can use...once they figure out how.
Follow Cheryl Kaye Tardif on Twitter. By following me, you'll automatically be entered in my Twitter Contest.