Hi!
Silverstripe sintax is a bit complex for me.
So my problem is take data return by function in my template.
If my function return a boolen, and I call $function_name in my template everything is ok.
But if I need a if structure link
<% if function return true %>
...
<% else %>

how can pass this value in template?

ok..I read that document. Now I write my function. If I write $Login it's ok but I can't write
<% if $_SESSION['user']=1 %> in my template.
this is my function:

function Login() {      
       if((Session::get('registrato', false))and($_SESSION['user']=1))
       {   return $_SESSION['user'];   
       }
      
    // Create fields
    $fields1 = new FieldSet(
    new TextField(
    $name = "nome",
           $title = "Username:",
           $value = ""
    ),
    new PasswordField(
       $name = "password",
       $title = "Password:",
       $value = ""
       )
        );
   
// Create actions
$actions = new FieldSet(
new FormAction('doLogin', 'LOGIN')
);

return new Form($this, 'Login', $fields1, $actions);
}

Weird that you're recreating the security system.

Why not use the existing security functionality. Then you can use:

<% if CurrentMember %>

from within your templates.

Then you can use the usual hooks:

<% if CurrentMember %>
Hello $CurrentMember.FirstName
<% else %>
You are not logged in
<% end_if %>

Have a look at:

http://doc.silverstripe.com/doku.php?id=permission