An array is a series of variables with the same name. Individual values, also called elements, in the series are accessed using an index. You can think of an array as a table with a column. The column contains cells, and in each cell is a value. You can save data to a cell, or retrieve data from the cell, using the row number (or index) in the table.
In the real world, programming usually involves groups of objects. Arrays are specifically designed to store groups of objects (the objects are retrieved using the index). Arrays are important because they make it possible to easily scale your code—meaning they deal in an automated fashion with the vast amount of data presented by the real world.
It’s common to first write a function (or program) to deal with a single instance of a value. The function can then be generalized, using an array, to deal with many instances of the same type.
Once you have the code working for a single value, it takes little additional work to create code that processes all the values in an array—so in this way it doesn’t take much more work to write code that processes many values after you’ve written the code that processes the first value. (Another way of saying this, in jargon, is that “the program easily scales.”)