To use jQuery libraries, you need to add a link on the HTMl page that imports them.
If you have download jQuery library and hosted it on yours servers, using <script> tag with an SRC attribute, you can add it with link on HTML page.
The jQuery library link is always placed above the link for the javascript file, for example:
<script src='jquery-3.4.1.min.js'></script>
<script type="text/javascript" src="myJavascript.js"></script>
Otherwise there would be a conflict between them and the jQuery library would not work.
Jquery libraries can be added to HTML pages in another way if they are imported by CDN (Content Delivery Network) from various servers hosted by jQueri.
Example jQuery CDN link: