To get two-page spreads by default you would need to select Facing Pages in the Document setup dialog, and specify more than 1 page. To have all pages in two-page spreads there must be an even number of pages and the start page number must be even, or you have to jump through a lot of hoops later in the pages panel.
You can convert an existing single-page master spread to two pages by opening the Master Page Options dialog for that master, but that will only help if you also change your document to facing pages in the document setup dialog.
I have done that selectino 2 pages in the document set up as well as facing pages. Yet the two pages the 2 pages end up on top of one another.
CS5 or CS5.5 once I selected facing pages and double page spread is in CS5 CS 5.5 i would get two pages as a spread . Not one page up and the next page down as if I have a 5 page document.