Many of my designs that are taught on this website require jQuery to work properly. Sometimes, on some wordpress websites, jQuery is not enqueued properly and you will get the error 'Uncaught ReferenceError: jQuery is not defined' in the Console.
If any of my designs are not working, open Chrome in incognito mode, then press F12 to open the console. If you see the above error, then fix it as follow.
To begin with, add this code to your theme or child theme functions.php , or to the plugin Code Snippet (my preference).
wp_enqueue_script( 'jquery' );
Here is what it will look like in a Snippet