Content Web Form not permitting to add content

This is the code of a nested master page in my project:

<%@ Master Language="C#" MasterPageFile="~/Presentation_Layer/Pages/home.Master" AutoEventWireup="true" CodeBehind="cmsNestedMasterPage.master.cs" Inherits="livetest.Presentation_Layer.Pages.cmsNestedMasterPage" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">

</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <div id="divMenuSideBarLeft" class="MainSideBar1Div" style="top: 2px" 
        title="LiveTest CMS Menu">
    </div>

 <div id="divCmsContent" class="MainContentDiv" title="divCmsContent" 
        style="background-color: ButtonFace; width: 791px; left: 203px; position:relative; top: -602px;">
    &l开发者_JAVA技巧t;/div>
</asp:Content>

I have following queries:

1. The first ContentPlaceHolder ContentPlaceHolderID="head", what is it for? Both the ContentPlaceHolders were automatically added when I added this nested master page to my project.
2. In the second ContentPlaceHolder with ContentPlaceHolderID="ContentPlaceHolder1", I added two divs. One is to display a side-bar on the left and the other is where I am going to show forms for entry. The problem is that when I added a new Web Content Form and linked it to this master page, it has only one pre-written line:

<%@ Page Title="" Language="C#"
    MasterPageFile="~/Presentation_Layer/Pages/cmsNestedMasterPage.master" 
    AutoEventWireup="true" CodeBehind="BookEntry.aspx.cs" 
    Inherits="livetest.Presentation_Layer.Pages.CMS.BookEntry" %>

The code is not showing any ContentPlaceHolders. Even if I try to add one, it gives error:

The page has one or more <asp:Content> controls that do not correspond with <asp:ContentPlaceHolder> controls in the Master page.

How to rectify this error?

You need to add ContentPlaceHolders to the nested MasterPage inside the Content elements. eg

MasterPage 1:

<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">

</asp:ContentPlaceHolder>

Nested MasterPage:

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">

    <div id="divMenuSideBarLeft" class="MainSideBar1Div" style="top: 2px" title="LiveTest CMS Menu">
    </div>

    <div id="divCmsContent" class="MainContentDiv" title="divCmsContent" style="background-color: ButtonFace; width: 791px; left: 203px; position:relative; top: -602px;">
       <-- Content on page goes inside this ContentPlaceHolder -->
       <asp:ContentPlaceHolder ID="cphCmsDiv" runat="server">
       </asp:ContentPlaceHolder>
    </div>

</asp:Content>

Then add the corresponding Content items to the page (they will be added automatically for new pages):

<asp:Content ID="Content3" ContentPlaceHolderID="cphCmsDiv" runat="server">

</asp:Content>