A data structure is a way of organising data so that it can be efficiently processed using simple algorithms.

An array is an example of a data structure.

An array is a 'list' of data items which are all the same data type.

The data items in an array are called its elements. 
Each element has a subscript to identify it (usually a number...but not necessarily).

A one-dimensional array is an array where each item is identified by one subscript.

Example : An array of strings called 'NAME' .

NAME[2] denotes the element of the array NAME which has subscript 2 - ie 'John Kingsley'.