text box not showing for author and comment

I have this code in show.html.erb when i load application it wont show text box for author and comment. not sure whats wrong.

I tried to change it to

form_for @book do |f|

But then i get error undefined method author

<h3>Post Your Comment</h3>
<% form_for([@book, Comment.new]) do |f| %>
  <p><%= f.label :author %></p>
  <p><%= f.text_field :author %></p>

  <p><%= f.label :text, 'Comment' %></p>
  <p><%= f.text_area :text %></p>

  <%= f.submit 'Save' %>
<% end %>