We'll say more about this later, but OpenGL maintains a current state that keeps track of information like the current drawing color, current line width, etc. This state is initialized at the start of the program and then modified by subsequent function calls defined in the OpenGL API.
The initialization of the OpenGL state is taken care of by the GLUT functions glutInit() and glutInitDisplayMode(). The first function takes as parameters the list of command-line options the program was started with while the second takes information used to initialize the frame buffer.