To Save as Template: I assume you wish to set this as your "page" area, and want to reproduce it throughout your site .... if this is so, merely size it to whatever page size is required, lay your elements on top of it (Menu/navigation, borders, etc.) and either use the CLONE icon to reproduce the basic page layout, or, individually strip and re-construct the page manually, being careful to SAVE each with a new title name.
To Save as Background: Re-size it to 1400 pixels wide and 1000 pixels deep, import it/set it into a blank page in BV, SAVE the page as bgimage and publish it to your account. Visit the page live online, right-click on it and "SAVE AS BACKGROUND" to a folder where you can get to it. When back in BV, right-click on your blank page, go to PAGE PROPERTIES >> BACKGROUND tab, and IMPORT IMAGE as BACKGROUND.
It looks like you need to go back to the Tutorials and pay attention to these basics .... there really is no need to constantly post for assistance in the forums on an issue-by-issue basis on things you should be able to understand via independent study of the given resources (like doing simple Forum Searches or even using Google to find things).... 