I've had at least 3 sources telling me stuff about Objects (the Sun tutorial, my cousin and my instructor), but the idea never really clicked until I figured it out for and by myself, so I'm not sure how much help I'll be, but I'll relay my understanding of OOP here.
subject to conceptual derp
So you have an object. In general, imagine it like a block of clay that you can stick stuff onto; it is nothing until you define it to be something.
By defining, I mean giving it characteristics, behaviors and a name/type. Characteristics are probably what's referred to as fields, behaviors would be methods and the type is just that: type.
So imagine an object called a... line. What properties does it have? Well, length, that's it. What does it do? Idk, not much, just hanging around chilling.
Now imagine a... car, classic.
What properties does a car have? Well, tons. Let's go with the easy stuff: horse power, mileage, number of seats, number of wheels, number of doors, etc...
What does it do? Well it surely can move, at least. More specifically, it can speed up, slow down, turn left/right, reverse, jump, toot its horn, flash lights, etc...
What's its type? Well, car, duh.
So that's a Car class (declared like so: public class Car {}), a Car object is there when you make an instance (an example, a unit, a single identity, whatever clicks for you) of that model. If you've heard of Plato's theory of Forms, the class is like the form of the car while each car object you make is a particular.
(Then you can have subclasses of the class Car, like a Sedan class where num_doors is declared to be 4, for example. But this is for later.)
So, you have a class Point. What does it spit out? Well, a point. What properties does a point have? Probably its coordinate (x and y, as in your code). What does it do? I don't know... move to a new position? So the action of moving is defined as changing its property of coordinates.
E.G: pointA would have x = 2 and y = 5. point A.move(2,3) would change pointA's x and y into 4 and 8 (2 + 2 and 5 + 3). Syntax is given above by Spaz.
The action of moving changes pointA's states directly and do not return any information, thus it is declared void (no return type).
For comparison, a method that might return something for the Point class is distanceFromOrigin(), which takes the object's (pointA's) x and y information, do voodoo magic to it then return the distance from the origin.
