Oreign Exchange Rates, International Trade, and End of National Currency

Answer the questions:

How do currency exchange rates effect individuals within a country? Even if some of them have nothing to do with foreign trade,etc?

What is arbitrage and why is it illegal?

Why would foreigners make foreign direct investments in the US? In China? Explain

Is the US better off when other countries use dollars as the basis of their currency system? Why?

Every time the U.S. Congress balks on an issue of the US currency(like the debt ceiling), what does this do to the US dollar as a global currency?