Default content will appear unless it is overridden in a particular content page.
File: Default.master
<%@ Master Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title>Default Master</title>
</head>
<body>
<form id="form1" runat="server">
<div class="content">
<div class="leftColumn">
<asp:contentplaceholder
id="ContentPlaceHolder1"
runat="server"/>
</div>
<div class="middleColumn">
<asp:ContentPlaceholder
id="ContentPlaceHolder2"
runat="server" />
</div>
<div class="rightColumn">
<asp:ContentPlaceHolder
id="contentAd"
Runat="server">
<asp:Image
id="imgAd"
ImageUrl="~/BannerAd.gif"
CssClass="ad"
AlternateText="Advertisement"
Runat="server" />
</asp:ContentPlaceHolder>
</div>
<br class="clear" />
</div>
</form>
</body>
</html>
File: DefaultContent.aspx
<%@ Page Language="C#" MasterPageFile="~/Default.master" %>
<asp:Content
ID="Content1"
ContentPlaceHolderID="ContentPlaceHolder1"
Runat="Server">
Content in the first column
<br />Content in the first column
<br />Content in the first column
<br />Content in the first column
<br />Content in the first column
</asp:Content>
<asp:Content
ID="Content2"
ContentPlaceHolderID="ContentPlaceHolder2"
Runat="Server">
Content in the second column
<br />Content in the second column
<br />Content in the second column
<br />Content in the second column
<br />Content in the second column
</asp:Content>