Any computer game starts with the idea and game world construction. That's what game design is dedicated to. Game design is a process of game content and rules creation. Good game design is concentrated on a gamer. It means that the gamer and his/her desires come first. Instead of guiding gamer's actions using rules, good game design encourages a gamer to move in a certain designer-defined direction. To set task for gamers to reach the opposite side or to raise level is just a task. If they don't have any reason or desires to do it, the game will become a torture. The role of game design in game development can be compared only with task setting in programming and director's activity in movie. 

In game creation process designers try to see the project from gamer's perspective: What is this game about? How am I playing? How am I winning? Why do I want to play? What is my next move in the game?