Audio monitoring can be tricky in FCP because both the program and the OS can control the signal path.
Quickest, dirtiest way to hear sound –
1. Disable external video in FCP under View>External Video.
2. In Apple’s System Preferences, be sure that Audio Output is assigned to Line-Out or Headphones.
If you are using an external video source (like a DV deck or a Kona card or such), you will need to route that audio to your speakers. This usually requires a mixer.
As far as learning the video formats – the way I did it was by lurking in the Cow’s FCP forums. Reading the daily pitfalls of others is the best way to have a working knowledge of tech.
Also, the FCP manual has a surprising amount of good info about video and audio tech, including good explainations of compression, video signal, all kinds of stuff.