The letters inside the square brackets, such as [A], refer to particular types of sexual activity. This is to give a better idea of what the stories contain. They are given in order of appearance in the text. Obviously, if there are no tags given, then there is no sex. A hyphen (-) before a label negates it; sometimes it's easier to state what isn't involved.
If more than one of a gender is involved, then a number before the letter will be used, such as 2M. This is to save space.
|DP||Double Penetration||F||Fellatio||FT||First Time|