gistfile1.rb

module FooModule
  def say_hello
    "Hello!"
  end
end

class FooClass
  include FooModule
end

FooClass.new.say_hello
# Hello!

module BarModule
  def say_hello
    "Hello from class!"
  end
end

class FooClass
  extend BarModule
end

FooClass.say_hello
# Hello from class!