It's all about programming

Most of the content of this book is about how to write computer programs. Apart from a brief introduction on how to make simple game graphics using Photoshop and Illustrator, I'm going to leave it to you to explore the graphics and illustration side of game design, which is well covered in other resources.

So what is a computer program?

A computer program is like a movie script that tells the characters and objects in your games what they should do and how to behave under certain conditions. For example, suppose that you designed a game in which the player must use the arrow keys on the keyboard to guide a duck through a pond infested with hungry snapping turtles. How will the duck know that it must move when the arrow keys are pressed? You need to write a program to tell the duck to do this.