Why does a country export products?

When a country exports products it is paid for them. The money received can then be used to import other products. So, for example, one country has coal but no onions, the neighboring country has onions but no coal. If the first country sells coal and buys onions, it can now make delicious sauteed onions. If the second country sells onions and buys coal, it too can make delicious sauteed onions. Everyone eats better.