Trade Embargoes are government actions to prohibit trade with another nations.
If the proposal is accepted by the Congress, it will be valid from the day it was accepted and lasts for 30 days. It's disabled automatically when the 30 days runs out. If desired, the president can propose another trade embargo with that country, and if it is accepted by the congress, the end date is delayed.
Note: The embargo is based on citizenship. If your citizenship country has a trading embargo with country X, you will not be able to sell products to country X's markets regardless of where you currently live.
Note: If you are a general manager and you have products for sale in that country, your offer will remain in the foreign market until you either remove it or the products sell out, but you will not be able to update the offer or create new offers whilst the trade embargo is active.
Note: Wars act like trade embargoes so always check the military page in your country.