In my opinion idea generation is the growth of an idea. The idea starts off as something simple or maybe broad, and as time goes on the idea changes, evolves, and gets better or worse. So basically you can relate it to a family line. Start off with the base of the family and then follow it through 3 generations and I bet you will be shocked at how the family line has changed and evolved whether it be for better or worse.
Also, idea generation may be as simple as generating ideas or brainstorming. Which means jotting down many ideas at once and from then picking out the better ideas until you get to a few ideas you like or a single idea you like that you can grow on.