The most important thing to remember about backgrounds is that whatever you place on a background page will be seen on every page of your document.

Also, backgrounds in Publisher are treated as separate pages.  Items on a background won´t move or wrap relative to things on the foreground.  So when you put items into a background (a logo, for example, that you might want to have on every page) you need to take into account where you will be placing information on the foreground page... even though, when working on the background, the foreground is invisible.

Move to the background by pressing CTRL+M.  Doing the same again will put you back in the foreground.  If you forget which one you´re in, you can check the status bar in the bottom left-hand corner of your screen:  if you can see a little double box with a red outline, you´re in background view.