Click a button and it should load the content into the main content area
<p>I have create 3 buttons on the left menu for "Cars," "Music," and "Games" 
When the user clicks one, it should load the appropriate contents into a DIV 
in the main content area. Each button should replace the contents of anything 
previously displayed in the div. I created my buttons, but I do not know how to 
load the content into the main content div or how to replace the previous content. 
Can you help please?</p>
