JQuery is JavaScript framework that provides shortcuts for everything JavaScript does e.g. DOM manipulation, AJAX etc. But, instead of typing out all those pesky document.querySelector(".cartMenu"), you use the shorthand $(".cartMenu"). It is so intrinsic to other libraries it is ubiquitous across the web.

Here are some samples that I hope you find useful...

Example: Get the <button> element with the class 'continue' and change its HTML to 'Next Step...'

            $( "button.continue" ).html( "Next Step..." )