An array is a list of a certain variable type, where each item in the list can be referenced by a unique index number, usually starting at 0. [...] Like any other variable type, PHP will automatically define a variable type and set it up for you when you start using it, however in most cases (and it's good practice) you should usually pre-declare your intention to use an array, especially if you don't know in advance what your going to be storing in it.

The article talks about what arrays are, how to create them, manipulating them with functions like array_splice and creating subarrays.