Adding new page to existing theme?

I installed a theme and now want to design a new page with a different design to have it available on my site. I want it to have the same style and look as the other pages, though I want the main content of the page to have a different look.

1.) What code do I put on the new page to link it to the CSS and header and main navigation of the other pages?

2.) do I just upload this new file to the location with all of my other files?

Thanks!!!