For the large part, jQuery is a querying language and uses CSS selectors to identify and update elements. Hence, if we are familiar with CSS, then we would certainly find ourselves very much at home.
Lastly, since jQuery is used with HTML, it would certainly be a good investment to become familiar with HTML. Various HTML elements are often represented using the Document Object Model (DOM) and knowing HTML DOM method would be a definite plus!
jQuery is primarily a querying language, where we use the jQuery() method (aka the $() method) to both locate an element on the HTML page and, if needed, to modify it. With jQuery, we can access page elements using HTML tags, CSS identifiers, and DOM.
Once the initial page is loaded, jQuery helps us in making the page more interactive by attaching event handlers to page elements. Event handlers add an asynchronous behavior to the page. In other words, the web-page does certain things only when certain events are triggered. As an example, we can add event to an image such that when we hover the mouse on top of an image, then it displays additional information. However, if the user does not move the mouse, then no information is displayed.
Next, jQuery also provides a rich support for creating animations, adding AJAX, implementing JSON, and providing a better UI. Last but not the least, we can also extend jQuery using plug-ins; these plug-ins provide various functionalities.
Before we go any further, let us give in to the temptation of writing a simple Hello World program. The example is simple and all it does is print "Hello World!" on the browser. Here is the example:
Lastly, the example calls jQuery APIs using jQuery() method or its more popular, the $() method. The $() method is actually a convenient shortcut to the jQuery function -- writing "jQuery(foo)" is same as "$(foo)"!