How to put a login form in the header for Devise and Rails

I want to put a login form in the header of my website. I use Rails 3.2.8 and the latest Devise. In the `app/views/devise/sessions/new.html.erb` file a login form is created with: ``` <%= form_for(resource, :as => resource_name, :url => session_path(resource_name), :html => {:class => 'main'}) do |f| %> <div><%= f.label :login %> <%= f.text_field :login, :placeholder => 'Enter username' %></div> <div><%= f.label :password %> <%= f.password_field :password, :placeholder => 'Enter password' %></div> <% if devise_mapping.rememberable? -%> <div><%= f.check_box :remember_me %> <%= f.label :remember_me %></div> <% end -%> <%= f.submit "Go" %> <% end %> ``` If I try to copy that code and put it in my `application.html.erb`, I get an error regarding that resource variable referenced above: ``` undefined local variable or method `resource' for #<#<Class:0x3cb62c8>:0x3c73b00> ``` So can I just use a normal rails form with `/users/sign_in` as the action? How do I tell devise where to redirect to after logging in?