First you set the array with 3 values. Then you say: change the first value (index 0) to a value of 3.
So you can acces a value of an element in an array (var myData = myArray[0]; or console.log(myArray[0]);), or change the value of an element in an array (myArray[0] = 3;).
@nigelFrancisNET: If you haven’t yet checked out MDN’s JavaScript documentation, you might find that helpful, as well. There’s an indexed collection in their JavaScript Guides on arrays. The whole page is helpful, and if you scroll down, you’ll see a discussion of multi-dimensional arrays with a chart that shows how indexing works. Hope this helps!