changing content for autenticated users? (using single-signon)

I have pretty much never used ASP.NET for a site that also used autentication.
but, for the company I work for, we want to have a fronend to a custom databasince, since I do have experiance with HTML/CSS and have used VB.NET before, I'm the one that gets to make it.
 
problem is, the one thing I have not used before is the autentication system in ASP.NET, I want to use single-signon for the system.
and I do have this right now, the only problem I have is how do I check if a user is logged in, and change the page content for autenticated users.
the template does have this:
<asp:LoginView ID="HeadLoginView" runat="server" EnableViewState="false"> <AnonymousTemplate> [ <a href="~/Account/Login.aspx" ID="HeadLoginStatus" runat="server">Log In</a> ] </AnonymousTemplate> <LoggedInTemplate> ...