I'd say the strongest example of it in current media would be Kevin Spacey's frequent lines directed into the camera in "House of Cards". Think about the difference between that and simple narration (in which a voice-over of the character talks about the story, but doesn't necessarily make the viewer feel like a member of the conversation.)

The difference is in the nature of the narration. Ordinary first person narration doesn't simulate a discussion with the reader. Fourth wall breaking narration directly poses hypothetical arguments to the reader (especially as a second person question), suggests they do things or look into things to improve their understanding of the situation, or even asks the reader to step outside to duke it out with the character over a presumed point of disagreement. It gets personal, like Kevin Spacey looking the viewer in the eye.

Hope this helped.

...
Regards,
Eric Fretheim
Assistant Prep Leader, 2015 October NaNoWriMo Prep Challenge

"It is perfectly okay to write garbage-- as long as you edit brilliantly." ~C.J. Cherryh

“No, writing 50,000 words in a month is normal. You are not crazy. This is not insane.” ~Teri Brown