A stock is bought or sold at a stock exchange. One of the largest stock exchanges in the world is the New York Stock Exchange. Every country has one or more stock exchanges used to trade stocks. Some of the other prominent ones include Tokyo, London, Mumbai, and Shanghai. Some highly volatile stocks with low market caps may be traded over the counter (OTC) and are commonly known as penny stocks. These stocks tend to be the riskiest stock investments, and fewer analysts follow them. They are traded on OTC Pink Sheets. If you are learning how to invest in the stock market, it is best to avoid penny stocks.