A stock exchange is a corporation or mutual organization which provides "trading" facilities for stock brokers and traders, to trade stocks and other securities. There are three main stock exchanges in the United States: New York Stock Exchange (NYSE), Nasdaq Stock Exchange (National Association of Securities Dealers Automated Quotations) and American Stock Exchange (Amex).
Naked options trading is very risky - many people lose money trading them. It is recommended contacting your broker or investment professional to find out about trading risk and margin requirements before getting involved into trading uncovered options.