Help Needed - Form Authentication

Dear Experts,

hey i'm newbie to asp.net, I'm using MasterPage In my Project,

It have 3 Content Place Holder namely Top,MainContent,Buttom respectively,

i have to use Form Authentication in my project,

Default.aspx page is an Startup Page which have the control to get username and password in MainContent controlplaceholder,

i declared in web.config file as follows

<configuration>
  <system.web>
    <authentication mode="Forms">
      <forms name=".COOKIEDEMO"
             loginUrl="default.aspx"
             protection="All"
             timeout="30"
     & ...