Populating the world is not a function of the game engine, but rather is something the game code does. Remember the tutorial's populateWorld() function? This was part of our "10,000" foot view of game code (bottom of page 13).
So, the game code does:
populateWorld() // the game developer writes this
For project2a, you, acting as the "game developer", will make some simple game objects (derived from Object) to populate the world with.