Diablo – How to link an item in the chat

Monster drops are seen individually,however once you pick up item and drop it again it can be seen by others,also not picking up items or leaving them on the ground will make them available to other players.

To make a proper trade you can right click on a player portrait and open up a trade window.

Not sure what you mean by placing item in a container :/ ...If you mean stash it is visible only by you,if you mean on the drops from crashing the barrels...It is the same as with monster drops.

Sadly, there's no way to create a custom chat channel in Diablo III and probably there will never be. Unless there's a big change, driven by players' rage, I don't think they're going to change their mind.