a. add to Gemfile
gem 'rails_marketplace'

b. bundle install

a. rake rails_marketplace:install:migrations
b. rake db:migrate

a. rails generate uploader ProductImages
b. add to app/uploaders/product_images_uploader.rb

  include CarrierWave::MiniMagick

  version :large do
    process resize_to_fit: [350, 500]
  end

  version :small do
    process resize_to_fit: [130, 160]
  end

  version :thumb do
    process resize_and_pad: [80, 80, "#ffffff"]
  end

a. add to `app/assets/config/manifest.js`
//= link rails_marketplace/application.css
//= link rails_marketplace/application.js 

a. add to config/routes.rb
mount RailsMarketplace::Engine, at: "/"
b. rails s
c. go to localhost:3000