Discussion Boards unite all of your SharePoint users to share information and ideas.  All of your users can start discussions or reply to current ones.
To create a discussion board go to Site Actions >> Create. Under Communications, click Discussion Board.
 
Give your Discussion Board a title, description, and choose whether you would like to display it in the Quick Launch bar.
To create a new topic, click New on the Discussion toolbar.
Give a title to your discussion thread, attach a document if you like, and type a message to get the conversation going. Click OK.

 
If you want to reply to a message, click on the message of choice.
 
Then the discussion will open.  You will be able to read what is currently in the body of the discussion and previously posted replies if there are any.  Click the reply button located in the right corner to post a reply of your own.
 
Type your reply in the body of the message and Click OK.  Now you get to play the fun part of waiting for a response or seeing if your response was even helpful.