form_for yags questions

Hi have a question about several tags, I do not understand if they are RoR tags os something else

this is my form, I wrote it following the book "Simply Rails 2" in chapter 6:

<% form_for @contacto do |f| %> <p><label>Your Name:<br /><%= f.text_field :name, :size => 25 %></label></p> <p><label>Your email:<br /> <%= f.text_field :email, :size => 25 %></label></p> <p><label>Message:<br /><%= f.text_area :body, :rows => 10, :cols => 30 %></label></p> <p><label><%= submit_tag 'Submit' %> </label></p> <% end %>

This is another form I found on "open source social network - from the apress book"

<%= error_messages_for :page %>

<% form_for :page, :url => pages_url, :html => { :method => :post } do

f> -%>

  <p>Title:<br /><%= f.text_field :title, :size => 60 %></p>   <p>Body:<br /><%= f.text_area :body, :rows => 20, :cols => 60 %></p>   <%= submit_tag 'Save' %> or <%= link_to 'cancel', pages_url %> <% end -%>

questions:    - is "error_messages_for" a RoR reserved statement?    - in this expression ":url => pages_url", where does pages_url come from?    - in this expression ":html => { :method => :post } " why o I need a post?    - what is the difference between using "@contacto" and ":contacto", in form_for. <% form_for @contacto ... or <% form_for :contacto