Select By CSS Class Name $(".className")

This jQuery selector selects elements by CSS class assigned to class attribute. For example to select element <div class='someClass'> use $('.someClass')

$(".className")

$(".className") selects all elements that have class="className"

.className is CSS class name defined in <style> or in CSS file, e.g. .className {color:#fff, width:30px} .
Example 1: $(".someClass") will select all elements with class='someClass'
<div id='someID'>div-1</div>
<div class='someClass'>div-2</div>
<p>p-1</p>
<div>div-3</div>
<span>span-1</span>

Demo: Find all elements with class='shape'

HTML & CSS
//CSS style
.shape{
    border:2px #000 solid; 
    background: #f0f0f0;
    ...
}

<div class="shape">DIV 1</div>
<div class="shape">DIV 2</div>
<div class="shape">DIV 3</div>
jQuery code
$(".shape");
Demo

DIV 1
DIV 2
DIV 3
jQuery selector $(".className")