Sorry - new user to PHP and Zenphoto. I've chosen Zenpages as a theme which I believe is built in but I want to edit it's contact page to just be an email link. But I can't find which page is the main page! Stupid I know.

The standard contact page for is a static custom page (see theming tutorial about that). It is the contact.php page within the theme you need to edit directly. There is an option to disable display of this so you can use a real Zenpage page to edit via the backend instead.