try applying your image to a master page. Doing so will make your image display on all pages using that master page. Unless you tell it to, the image is locked so it won't move when you add objects on top of the image.
I get the sense that you want different portions of a very large image to be on different pages. If that's the case, putting it on the master page will not work. Images on the master page will appear identically on all pages to which that master is applied.
To have a different part of the image on each page, the easiest method is to place the image across pages making up a spread. You can assemble non-facing pages into what "looks like" a spread on your screen by opeing the Pages panel flyout menu and unchecking Allow Document Pages to Shuffle (this will keep all pages from shuffling, or you can select individual pages and uncheck Allow Selected Spreads to Shuffle). Once shuffling is turned off, you can drag the page thumbnails in the panel and stick up to ten pages together horizontally edge to edge.
Regardless of how pages are arranged in the panel, they remain individual pages until output, and will only be combined at that point if you export to interactive PDF or specify "Spreads" in the PDF (Print) or Print dialogs. There is a script floating around the forum that will toggle OFF spreads for export to PDF(Interactive) as there is no option in the interface to do that.
The second part of your question is more difficult. There is no way to copy from InDesign and paste into an email and get anything that resembles the ID layout. You can export to HTML from ID, but that is essentially raw code that will require further processing to create a finished layout in HTML. You could export to PDF and add that to an email as an attachment, or put it on a server and include a link in the email, but if you want to have the newsletter itself be the layout, ID is NOT the program to use for building it. An easier solution would be something like MailChimp or ConstantContact.
+1 to all of Peter's comments.
If your aim is HTML emails you are using the a wrench when you should be using a screwdriver. InDesign is not the right tool here, Dreamweaver is.
But even at that, you'd be far better off with Constant Contact or MailChimp.
FWIW, here are my two recommendations for InDesign newbies:
1. Sandee Cohen's Visual Quick Start Guide should be on your book shelf. For $18 you can't go wrong: http://amzn.to/tcYOsj
2. Check out Lynda.com. This link will give you free one-week trial: http://bit.ly/fcGpiI