You create a Master Page in pretty much the same way as you create a normal ASP.NET page. A Master Page can contain the same Web controls, User controls, HTML content, and scripts that you would add to a standard ASP.NET page. There are three important differences between a Master Page and a normal ASP.NET page.
1. Master page should end in a .master extension
2. A Master Page includes a <%@ Master %> directive instead of the normal <%@ Page %> directive. The <%@ Master %> directive supports many of the same attributes as the <%@ Page %> directive. For example, you can specify the programming language of the page with the directive <%@ Master Language=”vb” %>.
3. A Master Page and a normal ASP.NET page is that a Master Page can contain zero or more ContentPlaceHolder controls. A ContentPlaceHolder control can be used only within a Master Page. This control marks an area of a Master Page that can be overridden by a particular content page.
Listing 1. Simple.master
Listing 2. Simple.aspx
Content in Left Column
Content in Right Column