We usually work with multiple things - print a list of groceries, add several numbers, etc.
We often repeat the same action on each thing in a group - frost a dozen cupcakes.
Ruby provides a couple of containers, plus ways to perform an action on each item in a collection.
goal "Hold multiple things with arrays and hashes"
goal "Loop over all the members of a group"
goal "Do a function to each member of a group"