This document discusses gameplay design for computer games. It explains that gameplay should be designed before story and graphics and defines gameplay as the core fun factor that should engage players. Gameplay involves challenges, which are objectives related to genre, and actions, which are player inputs. Challenges can include physical coordination, logic, math, time pressure, knowledge, memory, pattern recognition, exploration, conflict, economics, reasoning and thinking. Actions are verbs like accelerate, turn, jump. The document provides examples of challenge hierarchies and actions for different genres. It concludes by assigning a mission to design the gameplay for a game, including challenges, challenge hierarchy, essential and other actions.