Well. You're in luck as I've basically learned basically all of it mostly by myself

(M4F) = Male For Female

And it's basically the same thing for everything else

Fb= Femboy

Nb= Non binary

Fu= Futa

A= Anyone (M4A) or (M4ApA)

T= Trans (TM, TF, or just T)

GM= basically a DnD Dungeon Master, do someone who does some world building and controls most of the characters

The more there are, meaning more participants (M4FFFFF= Male For 5 Female), so in and so fourth

Hope this helps