newbie help: how do we actually trade?

This is a silly question, but I read "the bible" here and didnt see this (maybe I missed it).

I'm assuming that players agree to a trade here, and then go to the game online, seller creates a game and password, buyer shows up and they trade there.

Correct? I mean, there isnt a way to trade directly here, is there?

Correct.
Though, most people use Battle.Net friends list (when trade is agreed here they will say "adding you", that's the interest if verifying your BNet ID in your profile - also does copy paste on click) to join each other's game (so allows to simply use "play" button for game creator).

Just un-friend your trader when done. And always be reliable, of course.

Remember that most people use their mule characters for what they have at sale so 95% of trades are held in normal, act 1.

Welcome around !

and try to trade over the ingame trade menu. at least the worthy things...