Other way, if you have variable t , of class Triangle , and variable s , of class Square , you paint a triangle with t. Paint , and square with s. So, I came to the term object . Plain and simple, object is variable of some class. Other name for object is instance .
Class is type definition, object is particular specimen of the class.
If you have auxiliary piece of code that is called only by methods of class itself, you'll make it as private method - invisible from outside of the class. Hiding of code is called encapsulation . This is the key for code-reusability. Imagine you find an error in the first copy - that means you have to identically fix it in other copies as well. What a chaos if such libraries were written by simple copying the code.