Loading and Hiding images

Hello, I'm a newbie with a simple question that I could use some help on. I am writing code orginally displaying images on the screen, but when a pic is clicked I want another image to show up on the screen. What I would like do to is load all of the images, and keep some hiden until the appropriate pic is "clicked" on and then the image would become unhiden. I am having trouble with the coding on this, and have been looking for a document or a already posted forum to help, but since I could not find anything to answer my question directly I thought I would ask. Thanks for the help!