1. What is assets-pipeline

it provides the framework to concatenate and minify or compress JS, CSS assets
it can also write these assets in other languages and pre-processors such as CoffeeScript, Sass and ERB
it is implemented by gem sprockets-rails gem, and is enabled by defaut.

*** Fingerprinting technical

make name of file dependent on the content of file, file changed => name changed
it avoid query strings to reduce problems

Using assets-pipeline

At subdirectory : app/assets
Any assets under public will be served as static files by the application or web server when config.public_file_server.enabled is set to true.
In production, Rails precompile those file to public/assets by default. The precompiled copies are then served as static assets by the web server. File in app/assets never be run directly
if the coffee-rails or sass-rails is in Gemfile, when you generate the controller or scafford, Rails automatically generate .coffee and .scss file.
You can also disable generation of controller specific asset files by adding the following to your config/application.rb configuration:
(config.generators do |g|
g.assets false
end)