How the international trade raise the standard of living?

The theory of international trade is based off the idea of comparative advantage, which is based of the idea of opportunity cost

Opportunity cost is the value of the alternatives to a given action. Comparative advantage is the relative advantage that a person has for a particular task when his or her opportunity cost is lower than another person for the same task.

For example Country A can produce 30 computers and 20 chairs. Country B can produce 10 computers and 20 chairs. If Country A produces 30 computers then the opportunity cost is 20 chairs. If Country B produces 10 computers the opportunity cost is 20 chairs. If Country A produces 20 chairs then the opportunity cost is 30 computers. If Country B produces 20 chairs the opportunity cost is 10 computers.

Based on the analysis through comparative advantage, Country A should produce 30 computers because if it produces chairs then it will lose 10 computers that it would've produces. Countries practicing this kind of production imply specialization where one country should produce what is cheapest for it to produce. Through specialization goods are produced where they are the cheapest to produce and all the resources of that region are used as inputs for that good. Specializing also implies that countries have to trade because life requires a plethora of different goods.

Through trade each country can gain because if Country B produced computers it would not be able to make 10 chairs and would have to make less. When trade is implemented Country B can have more chairs and more computers than they would've been able to if there had been no trade. This logic can be applied to Country A where they can have more chairs and computers too.

All participants in trade benefit and their standards of living increases as there are more goods for everyone.