Can someone explain timecode?
 

So, I'm not 100% sure that this is the right place to post this question, but I couldn't find anywhere that seemed to make more sense.

Anyway, I recently interned on a feature film in the sound department (which was good, because sound is my weak point.) And I asked a lot of question, but a few of the answers never quite made sense to me.

The sound engineer was recording with a program called "boom recorder" and using a high power boom, and a couple of wireless lavs... which then went into a mixer and which recorded both onto the engineers mac, and the red one.

He said, he said this would let them start editing while he was still creating the final mix, because they gave everything a timecode. But if they edit all the in camera audio w/ the video, how exactly does he know what to mix? Or does he mix everything, then they find the pieces that they used from the total mix, and re-insert them at the correct place?

I hope I sort of made sense here... Anyone have any insight?

Also, how do you work a timecode? I.E. How do you make it in both audio and video, and connect, etc...

Thanks!