No, it is not somebody else’s game that you modify like “GameCreators”. Nothing like that at all. It is a “raw” set of tools and generic behaviors that are common to most game related tasks, such as moving objects, constraining them to paths, starting and stopping animation sequences, moving a joint, (open a door), start and stop timers, activating a spring reaction, starting a particle stream, modifying geometry and materials and textures, moving or rotating the view, jumping to a new location or scene, reacting to a collision, etc.
The triggers for these commonly used behaviors are also equally generic in nature. They can be attached to anything and include mouse location and state, keyboard presses, time, (local and global), position, orientation and scale of objects, as well as a change in any other existing parameter.
The entire system is infinitely flexible and offers an exponential combination of complex “cause and effect” events to happen, as well as random groupings of behaviors, making the kinds of gameplay that can be imagined and made “real”, unlimited.
The only difference between this method of creating games and creating games from scratch with raw code, is that one does not need to know how to code or think in code. One still must be able to work through the logic of the game play, but can instantly test any behavior they have designed visually, functionally, observably as a scientist would do in a laboratory, rather than as a mathematician would do on paper with symbology. This system is visual programming, graphic programming, process oriented and not at all cryptic in nature. This allows the speeding up of all game creation processes, giving the independent game creator a chance to finish what they have started rather than remotely fiddle with code. It is hands on game making, rather than hands off game making, which is what you have when using cryptic code to define behaviors and reactions.
This system is not a library of predefined anything - that you merely piece together to make something like a first person shooter. It is behavioral code encapsulated into visual representations that are common to “player” actions, whether the player is a character, an abstract object, a force, the “camera” , a group of objects or nearly anything you can imagine. You determine the exact nature of everything in the game, including its appearance, (any textured Blender model), its animated behavior, (keyframed and fine tuned by you within the creation environment), its physics or lack of them, and its ability to sense its environment, precise or random reactions to other objects in a scene, time, or location or orientation or any other parameter that exists.
Coding a game requires reinventing the wheel over and over and over again - very educational if what you are after is education. Not very practical for the individual, independent game developer that wants to get something done in a reasonable amount of time.