The letter stands for the fare class. F and A are generally first class (used to be some P first class as well). J, C, D, I, and Z are generally business class. The others (most of them) are generally economy. The letters have different meanings according to airline, etc., e.g. Z is heavily discounted business class on Northwest and Continental.

The number is the number of seats remaining that the airline is willing to sell for that flight. The 9 is the highest number, and if 9 is listed it means the airline is willing to sell at least 9 tickets for that fare class.

This is a fairly basic and inadequate (for an expert) explanation but it will give you a start. Research more thoroughly in your main airline's forum and you'll start to learn much, much more.