click on an element then loads a list

Hi

is it possible to load the list of images under the set 1 when a user clicks on set 1 and loads the list of images when clicks on set 2? how do you write onclick() ?

ul>
    <li><a href="#">set 1</a>
       <ul>
           <li><img src="1.jpg"></li> 
           <li><img src="2.jpg"></li>
       </ul>
    </li>   
   <li><a href="#">set 2</a>
       <ul>
           <li><img src="1.jpg"></li> 
           <li><img src="2.jpg"></li>
       </ul>
    </li> 
</ul>

Code (markup):

 

u have to explain it completely

 

sorry for not being clear. What I want to accomplish is something like this
http://www.cssplay.co.uk/menu/complex_slides
But I want to be click instead of hover on those #1, #2 ...etc. Do I have to use
onclick() ?