Add a page.

My question is very simple, but i´m doing some research and i cant find the answer.
What i need is this:
Create a new page, supose that my site is http://mygallery/main.php, my page's url must be http://mygallery/mypage.php, and i need to load some template that i already have, its just a search box, but i cant make all work, to sum up, all i need to know is how to load a gallery .tpl in a php file and make it work, isn't?.
How can i do this? I think that it's really simple, but i need to make it work really soon, i'll apreciate every coment.

Thanks in advance,
Carlos.