You've got the right idea, so here's how to go ahead: the onclick handlers run on the client side, in the browser, so you cannot call a PHP function directly. Instead, you need to add a JavaScript function that (as you mentioned) uses AJAX to call a PHP script and retrieve the data. Using jQuery, you can do something like this:
<script type="text/javascript">
function recp(id) {
$('#myStyle').load('data.php?id=' + id);
}
</script>
<a href="#" onClick="recp('1')" > One </a>
<a href="#" onClick="recp('2')" > Two </a>
<a href="#" onClick="recp('3')" > Three </a>
<div id='myStyle'>
</div>
Then you put your PHP code into a separate file: (I've called it data.php in the above example)
<?php
require ('myConnect.php');
$id = $_GET['id'];
$results = mysql_query("SELECT para FROM content WHERE para_ID='$id'");
if( mysql_num_rows($results) > 0 )
{
$row = mysql_fetch_array( $results );
echo $row['para'];
}
?>