This information relates to the source in the glest_main directory. The code is then organised into different folders; ai, game etc. Execution begins in the main/main.cpp file, specified by MAIN_FUNCTION(Glest::Game::glestMain); This tells the compiler that Glest::Game::glestMain function is the main function. You have 2 design patterns at the beginning, singleton and state. program.cpp contains the implementation for the Program Class. When the play button is pushed in MenuStateGameSettings the Game constructer is loaded with the gameSettings as an argument.