Since the 1980's a popular approach to programming has emerged known as Object Oriented Programming. This is a very powerful, yet simple, idea. In traditional approaches to programming there was a clear distinction made between data (that to be operated on) and program (the process that would operate on the data). The Object Oriented approach dispenses with this division.
An object is composed of both the data that describes it and the code that will operate upon it. As such, every object has within it everything it needs to go about its business. If an object is to be drawn it will draw itself. It will contain its own code for how to do that; it will not need to refer to or be acted upon by an external program.
That is the basic concept underlying Object Oriented thinking. However, there are a number of other very important concepts that accompany this approach.