How does the international trade affect the united states and other countries?

It increases the variety of products, among other things

Explanation:

International trade has many effects, but one of those, greatly positive, is to have the opportunity to trade goods from one country to another.  That allows a country who doesn't have one thing to buy that thing from another country and in return sell what he has a lot of to another country.

The most evident advantage of that is when it comes to food.  Without international trade, you wouldn't have bananas to eat, you wouldn't know the taste of chocolate and you couldn't put sugar in your cereals, because these products don't grow in the US.