Refresh textarea every few seconds that populates from MYSQL - php

Question

I'm working on a little PHP MYSQL chat app. I need to refresh the data in the chat window every few seconds without reloading the entire page. I know I have to use Javascript or Jquery to accomplish this but I don't really know them good enough.
Below is the code that creates the chat window and populates it from the database.
Thanks so much, appreciate the help.
<textarea id="screen" name="screen" style="width:100%;height:300;resize:none">
<?php
$sql="SELECT * FROM `$tbl_5` WHERE advertid='$advertid' ORDER by id ASC";
$result = mysqli_query($dbconn, $sql);
while ($row2=mysqli_fetch_row($result))
{
echo $row2[5]."\n";
}
?>
</textarea>
EDIT: My attempt using AJAX
<script src="http://code.jquery.com/jquery-latest.js"></script>
<script>
$(document).ready(function(){
sendRequest();
function sendRequest(){
$.ajax({
type: 'POST',
url: '/chatrefresh.php',
data: parameters,
success: function(response){
$('#chatwindow').html(response);
},
error: function(response){
alert(response);
},
complete: function() {
setInterval(sendRequest, 5000);
}
});
};
});
</script>
<table id="chatwindow" name="chatwindow"><tr><td></td></tr></table>
Chatrefresh.php
<textarea id="screen" name="screen" style="width:100%;height:300;resize:none">
<?php
include_once('session.php');
include('config.php');
$advertid=$_SESSION['advertid'];
$sql="SELECT * FROM `$tbl_5` WHERE advertid='$advertid' ORDER by id ASC";
$result = mysqli_query($dbconn, $sql);
while ($row=mysqli_fetch_row($result))
{
echo $row[5]."\n";
}
?>
</textarea>