Arrays are one of the built in DataTypes in JavaScript. They are on par, if not more useful than Objects. Arrays in JavaScript perform the function of Arrays and Lists/Vectors in other languages. Arrays allow you to traverse their contents in a serial manner using an index or allow random access to any element contained within them using array indices. Arrays in JavaScript can grow and shrink without the need to manually shift contents of the array.
The code for this lesson is present here:
Not bad. I however recommend against using W3Schools as a reference. See http://w3fools.com/.
MDN is just about the best resource available.
See: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array