Create new model, migration and manually insert data.

railsdb.rb

command to insert:
r = Rating.create :user_id => 1, :product_id => 1, :description => 'I dont like this shirt', :rating => 2

To run migration:
 bin/rake db:migrate
 
 To create anew migration for adding in reference columns :
 bin/rails generate migration AddUserAndProductToRatings user:references product:references

Create a new model/migration
 bin/rails generate model Rating description:text rating:integer