... Lines 2ff actually define the data used to describe the two cubes. You will rarely have to define anything in code like this. Usually, primitive shapes (spheres, cubes, and cones, for example) ... transformations ourselves. And it is not a pretty sight at times. Line 4 allocates an OpenGL context. This is used to keep track of all of our specific states, commands, and resources needed ... the former, it takes only a couple of lines of code to create a GLKView and specify various properties, whereas in those dark and unforgiving days before iOS5 , it could take dozens of lines...