A trade agreement is a deal between two clans agreeing the type and price of commodities to be traded. The details of such an agreement are not visible to the player, you simply set it up - the rest of the negotiation is implied by the other party's acceptance. Once agreed, a trade route is opened between the territory of your clan and that of your trade partner, enabling goods to be traded straight away for mutual advantage and profit. A trade agreement can be both offered and demanded.
A trade embargo is an agreement between two or more clans not to trade with a specified third clan. A trade embargo can be both offered and demanded.