Updating and return Php variables with javascript function

I want to clik on a my "klikme" div area and want to send a message to my php saying to add (or something else) to the variable and then return the output to my "output" div area. I tried ajax too but I ragequited and my process is gone forever. Here is my template:

index.php

<div id = "klikme">
        KLİK ME!

</div>

<div id = "output">
  <? include 'sayac.php'?>
</div>

sayac.php

<?php 
        echo $sayac = 5;

?>