class names are the elements of a css, its used to display the feature in-built of a css ..to apply a class name, u can use html tags like <div class= , <span class= , <a class= , <b class= etc..
It means that any content u insert on ur site with dat div class
will take the background of the div class for example <div class="div_class"> is now known as <div class="logo"> on that jcms css page
.