F, P are the letters most commonly used to indicate First Class.
J, C are the letters most often used to represent Business, or Executive Class.
Y is almost universally used to indicate a full fare economy ticket.
B, H, L, M, V, etc. are just some of the letters indicating subclasses (reduced, restricted, and/or discounted fares). These letters vary by airline and in value. On one airline B may be indicative of a more expensive ticket. On another airline L may represent a ticket booked on a seat sale.
X, U, R are a few of the letters commonly used to indicate a fare purchased from a consolidator.
If you have booked a discounted fare and are interested in the subclass you are holding, the letter immediately follows the flight number on your ticket and will fall under the heading of Booking Class or some similar, shortened version.
