The Trade command allows you to exchange items and gil with other players.
To initiate a trade with another player simply target and select him, and then select the Trade option that appears. The recipient of a trade request will receive an “Accept Trade” button. Selecting this will present the player with the options of “Accept”, “Refuse”, and “Close”. Choose “Accept” to accept the request.
Accepting a trade request will automatically open the trade window, in which both players set the items and/or gil they wish to exchange in the trade slots provided. To complete the trade process click “Accept”. Selecting “Cancel” will abort the trade.
There are more trading options in Final Fantasy XIV, the details of which you can find on the following pages: