I know about 12 inch font and courier type, but I'm submitting through email. Should I format it in book-fold view (so that it looks on-screen as though the actual book would) or in standard full-page layout?

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Most of the time they want it double spaced with one-inch margins. This makes reviewing and editing much easier. The publisher should have formatting instructions in the "Submissions" or "Instructions for Authors" section of their website. READ THESE! Improperly formatting will almost always get an automatic rejection (sorry to say).

Single page for sure. It is your writing that you're showcasing not how it is presented. Anything extra will just be a distraction. I hope this helps.

Unless the manuscript guidelines provided by your publisher specify otherwise, it is not necessary to put it in "book-fold" view. Just submit it as a Word document with a normal full-page layout. The reason you want to do this is because you don't know what trim size the pages of your book are going to be. After you submit your file, it will go through editorial staff and on to someone called a "compositor," who will arrange the text on the pages ("layout") based on the specifications ("trim size" or page size, margin width, font and font size, etc) of your book.