title: why form_for does not work for me
body: <p>(ruby 1.9.2 rails 3.0.6)</p>
  
  <p>I am new to ROR, sorry for my simple question.</p>
  
  <p>I have a form and a controller, when i launch my app, i can see the log have been displayed.. however there are exception when rendering the view...</p>
  
  <p>Everything should look just fine.. what is the problem? how can I fix it? </p>
  
  <p>Thanks.</p>
  
  <pre><code>undefined method `users_path' for #&lt;#&lt;Class:0x47c7678&gt;:0x47c6118&gt;
  Extracted source (around line #2):
  
  1: &lt;h1&gt;Welcome Aboard&lt;/h1&gt;
  2: &lt;%= form_for(@user) do |f| %&gt;
  3:   &lt;table&gt;
  4:     &lt;tr&gt;
  5:       &lt;td&gt;&lt;%= f.label :username %&gt;&lt;/td&gt;
  
  class RegisterController &lt; ApplicationController
  
    def sign_up
      logger.debug("sign_up inoked")
  
      @user = User.new
  
      logger.debug("sign_up finished")
    end
  
  end
  </code></pre>
  
  <p>views/register/sign_up.html.erb</p>
  
  <pre><code>&lt;%= form_for(@user) do |f| %&gt;
    &lt;table&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;%= f.label :username %&gt;&lt;/td&gt;
        &lt;td&gt;&lt;%= f.text_field :username %&gt;&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;%= f.label :password %&gt;&lt;/td&gt;
        &lt;td&gt;&lt;%= f.password_field :password %&gt;&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;%= f.label :password_confirmation %&gt;&lt;/td&gt;
        &lt;td&gt;&lt;%= f.password_field :password_confirmation %&gt;&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td colspan="2"&gt;&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td colspan="2"&gt;&lt;%= f.submit "Sign up" %&gt;&lt;/td&gt;
      &lt;/tr&gt;
    &lt;/table&gt;
  &lt;% end %&gt;
  </code></pre>