JQuery
The key to using JQuery is the <script> link to the library in the <head> section.
<meta charset="UTF-8">
<title>HTML JQuery</title>
<script type="text/javascript" src="http://code.jquery.com/jquery-latest.min.js"></script>
The link may also look like this:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
The JQuery library files can also be downloaded and accessed locally from this web site: