The .addClass() method allows you to add a class name to the specified element. If you want to add more than one class name you just separate each class name with a space.

$(".insetPP p:first-child").addClass("boldIt"); // this will add the class name of boldIt to the p:first-child in the element of class="insetPP"

<div class="insetPP">
    <p>The Title of the Book</p>
    <p>This is a very interesting work of literature</p>

When you use .addClass(), you need to be sure that this class exists in the stylesheet. If you just want to change some aspect, color, background, etc., you can also use .css(). The .css() method will add inline styling to the element. Inline styling can not be overwritten with stylesheet styling.

The class name will be added to the end of any other class assigned to that element.

The opposite of .addClass() is .removeClass().