As you surely realize by now, game development is quite complex and game design itself can be a very broad and elusive subject...
We might have just scratched the surface, but so far we've looked at how games are being produced, what kinds of teams make them, and what responsibilities a designer can assume within a development team.
Some games might have no real ending, but every game project has a start! We'll now put some of that industry knowledge into perspective, and start looking at how to work on a game idea and turn it into a presentable game concept.
And remember, your job is not to design the perfect gameplay system and walk away. You are there to help realize the game's potential and turn it into the best possible experience for your players. Put your personal preferences and biases aside and focus on what's good for the project, even if it requires you to scrap ill-fitting ideas and throw away weeks or months of work in the process.