In GDScript, arrays work like this:
var myArray = []
myArray.append(some_data)
for i in range(myArray.size()):
var array_data = myArray[i]
They can hold any data, and can change in size, so they're more like generic lists than they are arrays as understood in the C family. AFAIK there are specific array types for performance reasons. For lightweight work like getting a collection of nodes, you don't have to worry about it.
With that said, if you're storing variables of a single object in an array, it might make more sense to either just use the variables directly from the single object, or to store the variables in a dictionary:
var myDict = {}
myDict.some_data_A = obj.A
myDict["some_data_B"] = obj.B
var important_variable = myDict["some_data_A"]
var other_stuff = myDict.some_data_B
Arrays are poor choices for storing data where you'd like to know what sort of data is stored where, since it's very easy to forget what position 16 in your array is supposed to represent. You want arrays where you don't particularly care what each position represents; dictionaries do a better job at helping us remember what a particular key represents thanks to their being named, but consequently there's no guarantee of order so a for loop is no good on them (I mean, you could name each key by ordered integers, but then you may as well use an array.)