lol, I have to say it makes me so nervous when people here are saying that they have never seen it done well . . . considering that's what I write . . . still someone asked for an example so I might as well use one from my own work:
"They ran far from the house, now entirely swallowed by flames. They ran till they were very far away and then stopped. They stopped because this is where they were supposed to meet the third man. I'm sorry, I just realised I forgot to tell you that there was a third man, and the third man was the most frightening and dangerous one of the lot".
So you see how the narrator interrupts the story realising that they had told the story incorrectly. When I read this bit to kids, often they ask me after if the forgetting thing is actually written into the story, or if I had actually forgot (because obviously they aren't reading along, just listening). It's cute.
Here's another version of authorial intrusion:
"For, late that same night, having nowhere else to go, and not enough money to stay in a hotel, Mr. Underwood arrived at Alex's uncle's doorknob shop and asked if he could stay. And this an Important Development because I suppose you could say that this is where our story truly begins."
Once more the author is in there "I suppose you could say".
And lastly here is an example of the all knowing narrator, the one who knows stuff that no one else in the story does: "And what was even weirder was that sometimes it seemed as if they could practically read each other's minds. This probably had something to do with the fact that they were twins. But they didn't know this. And never would. Which is just the way things happen sometimes."
Anyway . . . that was just using me as an example, I hope that makes it a bit clearer (btw, these all come from an already published book, so I would really rather people not tell me how to fix them or whatever as it is just a little bit too late, lol).