Linking to a Theme File

Hello, I just copied the index.php file in the theme folder, made a few changes, and uploaded it with a new name.

So now I have index.php and newpage.php. The index.php is set to only show category 5 posts, where newpage.php is set to only show category 8 posts. Besides that, they’re identicle.

How do I make a link from index.php to newpage.php?

Thanks.