How to get posts posted by a user on page without refreshing the page using jQuery or AJAX?

[Jan Dvorak]

They simply ask the server periodically, "is there something new? The last I know is the message #3018534e". The server responds something like: "sure, there's a message #3018534f by 'Honnza' saying 'They simply ask ...'. It was posted at 9.9.2012 10:31 UTC".
The communication language is typically JSON (javascript object notation), so the query often looks like
GET chat.php?ajax=getMessages&after=3018534e
(note that the URL specifies the user javascript is making the query and the server should respond in JSON instead of sending a web page.
and the server responds with
[{
"msgID":"3018534f",
"author":"honnza",
"body":"They simply ask ...",
"date":"12:31:00 9.9.2012"
},{
"msgID":"30185350",
"author":"mr.T",
"body":"IDK LOL",
"date":"12:31:04 9.9.2012"
}]

Look up JSON, AJAX and jQuery (namely jQuery.get).