Ideally free trade should benifits everyone, but because of the way the US economy is set up, it only benefits people who are the heads of large corporations. In fact, in the US, it makes life more difficult for people because it reduces the number of jobs availble. It also has little to do with what goods are availble.
Free trade is a rigged system that only helps a small group of people: the wealthy. Wealthy individuals are able to arrange free trade in a way that benefits themselves. They do this by promoting practices like loose tax laws and business conglomerates. These practices help increase their wealth while leaving the poor in the dust.
Free trade allows country A to export more to country B and vice versa. Now, only a few companies from country A might export products to country B, but as those companies export more, they contribute to economic development by hiring more people. Any time unemployment rates fall, society as a whole benefits.
There are some immediate benefits of free trade, which often seem to work to the advantage of a select group of people However, some argue that restrictions on foreign trade, including tariffs and quotas eventually work to the detriment of American consumers and producers. Limiting trade limits what people can buy, and in a sellers' market, they can set the prices, which can work against folks who have less money available to spend.