Routing for has_and_belongs_to_many Association

Rails
1

I got two models, Book and Word.

class Book < ActiveRecord::Base
has_and_belongs_to_many :words
end

class Word < ActiveRecord::Base
has_and_belongs_to_many :books
end

I got a Join Tables for has_and_belongs_to_many Associations

class CreateBooksWords < ActiveRecord::Migration
def self.up
create_table :books_words, :id => false do |t|
t.integer :book_id
t.integer :word_id

  t.timestamps
end

end

def self.down
drop_table :books_words
end
end

Now I want to create Routing, and user can insert words for a book.
How do I do that?