gistfile1.rb

module MyModule
  def self.included(base)
    base.extend(ClassMethods)
  end

  def hellofrominstance
    puts "hello from #{self}"
  end

  # Conventionally named ClassMethods
  module ClassMethods
    def hellofromclass
      puts "Hello from #{self}"
    end
  end
end

# including MyModule will call the hook (#included) which
# extends the class methods
class Blah
  include MyModule
end

pry(main)> Blah.hellofromclass
#=> "Hello from Blah"
pry(main)> Blah.new.hellofrominstance
#=> "hello from #"