Some example use cases of jQuery include: sliders, lightbox popups, rotating testimonials, etc.
Using jQuery, developers can perform certain actions right in the browser without reloading a page. Some of these actions include navigating a web page, selecting elements on a page to perform actions on them, call Ajax scripts, and handle events like what happens when a user clicks an element.
To call jQuery in WordPress theme or plugin, users need to add their own jQuery scripts and enqueue them in WordPress. While enqueuing their scripts, users can call jQuery core or any jQuery plugin that comes with WordPress as a dependency. WordPress automatically loads it along with the user script.