jQuery : Introduction To Selectors

A very common task when using JavaScript is to read and modify the content of the page. To do this, you need to find the element(s) that you wish to change, and this is where selector support in jQuery will help you out. With normal JavaScript, finding elements can be extremely cumbersome, unless you need to find a single element which has a value specified in the ID attribute. jQuery can help you find elements based on their ID, classes, types, attributes, values of attributes and much, much more. It's based on CSS selectors and as you will see after going through this tutorial, it is extremely powerful.

Because this is such a common task, the jQuery constructor comes in several forms that takes a selector query as an argument, allowing you to locate element(s) with a very limited amount of code for optimal efficiency. You can instantiate the jQuery object simply by writing jQuery() or even shorter using the jQuery shortcut name: $(). Therefore, selecting a set of elements is as simple as this:

$(<query here>)

With the jQuery object returned, you can then start using and altering the element(s) you have matched. In the following chapters, you will see examples of some of the many ways you can select elements with jQuery.

Source:http://www.tutorialsdesk.com/2012/08/jquery-introduction-to-selectors.html