where to put jquery files code example

Example 1: include jquery

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

Example 2: how to import jquery in js file

var script = document.createElement('script');
script.src = 'https://code.jquery.com/jquery-3.4.1.min.js';
script.type = 'text/javascript';
document.getElementsByTagName('head')[0].appendChild(script);