Gifts and TradesCards in your hand, including exposed Plots, may be traded or given away at any time, except when a privileged attack is under way. Cards from your hand must go into the hand of the player who gets them.
You may not give away undrawn cards from your decks!
Cards in your Power Structure may be given away -- see Moving Groups, above.
A trade is just an exchange of gifts. If two players agree to a trade, the deal is binding if they make the exchange immediately. A deal is not binding if it involves a promise of something in the future.
Example: If you say, "If you give me the Boy Sprouts now, I'll give you a Plot card," and the other player gives you the Boy Sprouts, you must give him a Plot. But if you say, "If you give me the Boy Sprouts now, I'll give you a Plot card next turn," and he hands them over, you can break your promise next turn if you want!