The priming pan holds the priming powder, and the frizzen closes down over it, containing the priming powder in place until you fire the gun off:
http://en.wikipedia.org/wiki/File:Fl..._animation.gif
With a proper, tight-fitting frizzen you can move the gun around as much as you like, hold it upside-down or whatever, and your priming won't fall out. Towards the end of the flintlock era, there were even water-proof pans!
Knapped flints are shaped by hand by tapping at the right angles, using small steel tools, and are the most common. Some flints are sawn into shape. I never tried one of those.
The life of a flint really depends upon the lock. 30-50 shots is probably average, and you can re-knapp the flint edge yourself for more shots!
More guys should try flintlocks! They are not a mysterious art, and are quite reliable...!