A multi-dimensional array or nested array is simply an array within an array.
Example (non prettified layout for simple viewing):
So, to access "Boston" using bracket notation, we must keep zero indexing in mind and count the number of arrays inside the array up to where our element is located, so that would be . Then we need to count the number of elements in the array up to the position of our element, so that would be .
Now let's turn up the heat and add a bit more nesting to really challenge ourselves to see if we can still figure out how to access the elements in our deeply nested array.
 refers to the array containing "London"
 refers to the element in the third position which is the array containing the string, "English".
 refers to the first element inside of that array which is "English", therefore that string gets printed to the console.
Try accessing the population of Boston or nesting more arrays and then accessing those values to really challenge yourself. Feel free to add more cities or elements as well.