South Africa is much more efficient in the production of wheat the Japan but both countries need both products so it makes sense for South Africa to provide japan with South African Grey tweet in exchange for DVD's made in Japan
if each country concentrate on producing what it's naturally good at
if they specialize in that good both countries can then trade with each other
an end up with more both products and if they try to produce it all themselves
the consumers in both countries also benefit
because they will be buying products: made by the most efficient producer
and according to the economic theory