One way to implement what you need would be to use a Frame and then load
XAML defined pages (just set the source for the Frame to the next page). The
Frame will be just one of the elements in your window, you can have
StackPanel and other content there too (and you can use Grid, StackPanel,
etc. to arrange the Frame position).
Another way is to use a NavigationWindow for container and add Pages. Then
you can use the NavigationService to move between page. This can provide you
a little bit extra power as the NavigationService works similar to your
browser. It can go back and forward between pages (with GoBack or GoForward,
or directly Navigate).