Try your local library and check for keywords such as "flight gear". I seem to recall finding a few coffee-table style photobooks with information and "official" naming of each piece.
As for the reason for oxygen masks: as you go higher, the air gets thinner. Oxygen starvation can frequently lead to "doping" - not being aware of your situation, plane attitude, etc. - and unconsciousness. It happens to mountain climbers, too.