Ruby on rails devise form helper

I'm starting with ruby and rails and I want to create a helper to show this form :

<%= form_for( :user, :url => session_path( :user) ) do |f| %>
<%= f.text_field :email %>
<%= f.password_field :password %>
<%= f.check_box :remember_me %>
<%= f.label :remember_me %>
<%= f.submit 'Sign in' %>
<%= link_to "Forgot your password?", new_password_path( :user) %>
<% end %>

So I just have to call my function show_login-form and display my form :) but I don't know how :(

Thanks