A conventional program is a universe populated by a variety of different things; integers, real numbers, strings, arrays, functions, and so on. In contrast, an object-oriented program is very orderly. An object-oriented system consists of objects. Each object is like a minature computer. It is a specialized processor charged with performing a specific task.
Thus, my florist Flo is an object that provides the flower ordering service. The driver in my friends city provides the delivery service, and so on.
As part of their job, every object may require a small amount of memory, just like a miniature computer. The contents of this memory will, in a pure object-oriented language, be other objects. Thus, the entire universe is filled with objects.