Oh boy, that is a long list. xD
Pounding ones should appear if the Good bar is quite full and red hearts appear around Gomamon. Apology appears if you perform Harassment actions and need to apologize. Harassment actions (Molest etc.) appear when you do some Naughty Talk. Idle Chit-Chat makes Explore appear that handles many scenes. Arousal is when the arousal stat is high, but no art yet as for several of these scenes anyway. Actually, if you have not even touched Explore or Harassment, then it sounds like you have barely started playing yet. The Ending Guide in the description up there is for the secret scenes. Ruin and Fun is when the bar is full or quite full and one did some talking and outfits came up. If you can equip an outfit, you can unlock either of these two scenes, depending if the Good or Evil bar is full.