How does trade work?

I’m very new to the game, and was playing as Bohemia. There are lots of good I could not produce enough of or at all (notably, fabric). So, I built some trade centres.

I’m not sure how it works, but that didn’t. Maybe it’s because I didn’t have any merchant marines, but I’m land locked so I don’t know what to do in that situation.

I know there has been a major update to trade in the games history, but can someone let me know how it works? From my understanding I can’t directly trade for a specific good.. annoyingly.

Thanks!