Technically speaking the Blender game engine is a framework with a collection of modules for interactive purposes like physics, graphics, logic, sound and networking. Functionally the game engine processes virtual reality, consisting of content (the world, it's buildings) and behaviors (like physics, animation and logic). Elements in this world - also called GameObjects - behave autonomously by having a set of tools called LogicBricks, and Properties. For comparison, the Properties act as the memory, the Sensors are the senses, the Controllers are the brain and the Actuators allow for actions in the outside world (i.e. muscles).
At the moment, the Controllers can be scripted using python, or simple expressions. The idea is that the creation of logical behavior can be edited in a more visual way in the future, so the set of controllers expands with AI state machines, etc. Controllers could be split in control centers, like an audio visual center, motion center, etc.
Options from the GameMenu
Start the game engine, stop the engine with ESC, Blender will return to the Creator.
With this option checked the game engine runs without dropping frames. This is useful while recording to a Targa-Sequence or when you need to make sure that all collisions are calculated without loss on slower computers.
With this menu option checked, the game engine will show some information on how fast the game runs and how the work is distributed.
With this option checked, all Properties marked for debug output ( ) are printed on screen while the game engine is running.
Enable Autostart for the scene.