Your Facebook Wall contains posts that are visible to your friends, their friends or everyone, depending on how you configure your security settings. If you want to communicate with one of your Facebook friends without the conversation appearing in public view, posting on either Wall is not advisable. Use the private message system on Facebook for private communications.
Log on to your Facebook page. Click "Messages" in the menu bar on the left side of the screen. Click the "New Message" button in the top-right corner.
Enter the name of the person you want to send a message to in the "To" field. Input a subject line in the specified box, then type your message.
Click one of the corresponding icons at the bottom-left corner of the window to include an image, video or URL link in the message. Click "Send" when you are finished.