how can i use master pages with multiple child pages which i

i am trying to use my own master page with menu which are containing multiple page with each menu click.
but the problem is the page are open in their own .aspx extension and outside from the sitefinity but my requirement is that the page is open as just like under the sitefinity.

assume you have the master page with menu and each and every menu click open a .aspx page but the page i want open in under the sitefinity and actually the page is open as separate from the sitefinity
 Plz help me
thanks