F P A = First class
F for example on LH and UA, P on SQ and NZ, A is as far as I know only used by UA for discounted F (RTW) or for US segments on int'l Biz class trips, which entitles to sit First Class - booking class being A
C J D = Biz (D = discounted)
Y = Coach full fare

all others are "just" coach classes. Which letter is for the deepest discounted tix varies from carrier to carrier and doesn't follow any logic. Letters are quite often followed by some other codes, which usually describe the restrictions.

V WE14, which could mean
booking class V Weekend Stay required, 14 days advanced purchase.