Transition

Hey fellas, I was wondering if you could help explain how to put this transition together. I am looking to use it for a photo gallery, and I think it would put the finishing touches on the project I am working on. If you go to http://www.templatehelp.com/preset/pr_preview.php?i=14290&pr_code=ck1s8w2u54aeaY9y62IWQ99K6M5Kvp and click on any of the subpages you will see the transition I am talking about. If it is too complicated to explain I can buy the template and just see how they did it, but I figured I would come here first since you guys seem to always know what you’re talking about.

Thanks