Necessity of Foreign Exchange

No country is self-sufficient in this world. Every one is more or less dependent on another, for goods or services. Say, Bangladesh has cheap manpower whereas Saudi Arabia has cheap petroleum. So Bangladesh is dependent on Soudi Arabia for petroleum and Saudi Arabia is dependent on Bangladesh for cheap manpower. People of one country is going to another country for Education, Medical service etc. One country exports agricultural commodities, another country exports industrial products. All these transactions needs foreign currency & are related to foreign exchange.