The message activates that method. If the method called in this way happens to be a function, it will send a result value back to origin of the message. Computational objects, somewhat like real-world objects, have to be created. Once they are created, they continue to exist even when they are not receiving any messages. In fact, unless they are explicitly destroyed by the program, they exist as long as the application program which contains them is running.
Objects can own other objects.
A has some property, call it PROP, which has B as a value. In an object oriented environment, it is very important to know the hierarchy of objects, because refering to an object requires knowing where it is in the hierarchy, just as referring to a file requires knowing where it is in the hierarchy of folders. Hence, before working with the objects of NN, we must examine what objects there are and how they fit together into the NN object hierarchy. The active window is a display object, and the full NN window that you see on the screen is its display area. For the present we will ignore the problem of how to reference windows other than the current window.