Map takes a function and a collection of items. It makes a new, empty collection, runs the function on each item in the original collection and inserts each return value into the new collection. It returns the new collection.
This is a simple map that takes a list of names and returns a list of the lengths of those names:
name_lengths = map(len, ["Mary", "Isla", "Sam"]) print(name_lengths) =>[4, 4, 3]