Using timecode, LTC, SMPTE on a film set

Hi I'm getting into recording and editing audio for film and video, and I'm trying to understand about timecodes and SMPTE and LTC, etc. I have experience in the studio with music production. I also have live music/sound experience. I have a couple of questions that I was hoping to get some help with. I've tried doing some googling myself, but I can't find any good introductory articles.

1) How do timecodes work on film, especially when syncing camera footage and audio when a separate audio recording unit is used? How does SMPTE and LTC work? I looked up some of this info on Wikipedia but the articles are fairly technical and not that helpful for someone who is new to the industry.

2) Where does the clapper fit in with respect to syncing audio and video? I always thought the clapper was used to sync the start of each take by lining up the clap sound on the audio file with the clap motion on the video file. Of course this manual process can be tedious when working with multiple cameras/angles and many scenes and takes. But if the clapper is used to manually sync audio and video, what's the point of a timecode, and especially a timecode generator?

3) What should I look for when buying a recording unit for on-location recording? I understand this is better than using the camera's built-in audio recorder as most non-pro cameras (DSLRs, digital camcorders, etc.) will have fairly poor built-in pre-amps. Should I consider buying a separate pre-amp in addition to a recording unit? Or will most pro units have a decent built-in pre-amp?

Thank you so much for any help you can give me.

David H. Watson
dEhiN Entertainment