Re: What is difference between class and object
Class is a description of something, like an architect's plans and an object is like a house described by those plans. In software creating an object means using the 'new' keyword. If you haven't used 'new' you probably haven't created an object.
Understand that software objects, like like real objects can have a state, contain information and/or perform a function.
The Person class is a type of 'information only' class that doesn't have any functions. I think of that like a government form. The class defines the empty fields. When a clerk pulls out a blank one and fills it out now its an object and the information (name, age) are contained in that object. It can get passed around your program exactly like a physical form can get passed around an office, modified, filed, sorted, taped onto a box so it's linked to that 'object' etc.
More complicated classes also have functions and I think of them like a tool, say an adjustable wrench. This is an object which contains information (the state of adjustment of its jaws) and has functions (tighten, loosen). One part of your program can create the wrench and adjust its jaws, then pass it to another part of your program to use it.
Good program design for a big program will be divided into objects exactly like an assembly line is (painting machine, cutting machine) and will pass the objects between those steps (the important thing being built as well as order forms etc to control and manage).