[Plugin: WP-Choose-Thumb] What is Outside the loop for?

Here is some info about the loop:

https://codex.www.ads-software.com/The_Loop

Placing the thumb code outside the loop requires the id of the post the thumbnail is attached to. Not necessary for standard theme development.

Im a noob and learning as I go along. For the thumb nail plugin to work, where do I put:

<?php if(function_exists(‘wct_display_thumb’)){ if(!wct_display_thumb()){ /* Optionally add code for no thumbnail. */ } } ?>