I've been on this site a long time but how do I start a topic?

u just started one..

what you did is a topic. it is like a comment, except it's mangago and it's claled a topic. you can only do this on any story main home page whatever it's called.
example: you are currently on this story
----- "Mangago 'How To' Guide"
you scroll down to the bottom and you can create a topic there.