Right click on your solution explorer. Add Master page, designed it as your requirement
Than when ever you add another .aspx page at that time Add new item dialog box there are checked select master page checkbox
check the design of that page if u used login details there are content place holder master checked it.
than your child page coding in
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">