How do I use the Enumerable mixin in my class?

The Enumerable documentations says the following:

The Enumerable mixin provides collection classes with several traversal and searching methods, and with the ability to sort. The class must provide a method each, which yields successive members of the collection. If Enumerable#max, #min, or #sort is used, the objects in the collection must also implement a meaningful <=> operator, as these methods rely on an ordering between members of the collection.

This means implementing each on the collection. If you're interested in using #max, #min or #sort you should implement <=> on its members.

See: Enumerable

It's easy, just include the Enumerable module and define an each instance method, which more often than not will just use some other class's each method. Here's a really simplified example:

class ATeam
  include Enumerable

  def initialize(*members)
    @members = members
  end

  def each(&block)
    @members.each do |member|
      block.call(member)
    end
    # or
    # @members.each(&block)
  end
end

ateam = ATeam.new("Face", "B.A. Barracus", "Murdoch", "Hannibal")
#use any Enumerable method from here on
p ateam.map(&:downcase)

For further info, I recommend the following article: Ruby Enumerable Magic: The Basics.

In the context of your question, if what you expose through an accessor already is a collection, you probably don't need to bother with including Enumerable.