First thing, armor is specific to your primary profession, so if you are a warrior, you can only have warrior armor. Here's a link to the wiki about armors:
http://gw.gamewikis.org/wiki/Category:Armor everything you want to know should be in there. Cuirass refers to the chest piece of your armor.
As for trading, you have to advertise what you want to sell/buy and also what you want/offer in exchange for those items. Trying a random trade won't work since the person has no idea of what you are looking for. Also, no one will buy a weapon that isn't max damage with good mods. People usually trade for rare skin weapons, green weapons and some rare or expensive crafting materials, miniatures and a few other items that usually come from high-end areas. that you don't really have access to until you reach level 20 on one of your characters.
