使用带有PDO的单击按钮

I am very new to PDO. I want to show my entire table if someone clicks on a button. I have the right code to show the table, but I don't know how to incorporate the button.

<?php

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    //the code you already have goes here
 }else{ ?>

<form method ="post">
  <input type="submit" value="click me"/>
</form>

<?php }