The 'random' dialogue (Non-player dialogue) is in the other tabs of the quest window. Mainly combat, detection, and misc. Within each are subtypes that you can create, within you can make infos.
For example, in the Combat tab, you can select the subtype 'Hit'. Then any info's you create here will be played when valid NPC's (One's with your voices) get hit. There is also block, taunt, etc. Fill all of these out with dialogue, and make sure the quest is running when you need that dialogue. (Generic dialogue like this should usually be made in it's own seperate quest, that runs constantly no matter what)
There is also the Detection Tab, which contains all the stealth related dialogue. NormalToAlert, for example, is dialogue for when the NPC goes from Normal (Unaware) to alert. Things like "Huh, what was that?"
Then finally there is the Misc tab. This contains the most common 'civilian' dialogue, like for when the player knocks stuff over, or jumps on furniture. However it also contains 'hello' which are the greetings the NPC can say.
Experiment with filling in these three extra tabs, and you'll see your NPC's come to life!