Flex introduces a new concept where you don't go to different
pages. Flex has forms (see the <mx:Form> container). I would
say the Flex equivalent to "pages" can be achieved with a ViewStack
(see <mx:ViewStack> navigator container).
Take the classic online store example. In an HTML application
you would go a page that has items to purchase. You'd pick Add to
Cart and the page would refresh, showing your cart's contents and a
link to continue shopping. In Flex, your cart would be a panel on
the side of the screen and the catalog a List in the middle. You
could either drag items from the catalog onto the cart area
(probably a DataGrid) or click an Add to Cart button. But you
wouldn't get a page refresh. It would be quick and smooth. When you
check out, the catalog would slide out of the way and your cart
would expand to allow you to enter your shipping address, credit
card information, etc. to complete the shopping experience.
With a complex application however, you should design your
application using Flex Modules. This allows you to download only
those parts the user wants. For example, you might be writing an
insurance application with many types of forms. Each time soneone
uses the application, only a handful of forms would be needed.
Instead of loading up your 1,000 forms into the browser (which
would take some time) you load only those the user requests.