A stock market is a collection of exchanges where people buy and sell shares of publicly traded companies. Think of it like a massive, organized auction house. Instead of art or antiques, the items for sale are tiny pieces of ownership in companies like Apple or Ford.

Companies sell these shares, also known as stocks, for a simple reason: to raise money. This money, called capital, helps them grow, fund new projects, or hire more people. For investors, buying stock is a way to own a piece of that company's future success. If the company does well, the value of its stock may go up. If it does poorly, the value may go down.

Stocks don't just appear on the market. They are introduced through a specific process that involves two distinct stages: the primary and secondary markets.

After the IPO, the action moves to the secondary market. This is the stock market most people are familiar with. Here, investors trade those shares among themselves. The company is no longer directly involved in the transaction. When you buy 10 shares of a well-known company, you're almost certainly buying them from another investor on the secondary market, not from the company itself. The prices here are driven by supply and demand.

These transactions need a place to happen. That's the role of a stock exchange. An exchange is an organized and regulated marketplace that ensures trading is fair and orderly. It's the infrastructure that connects buyers and sellers.

Two of the most well-known exchanges in the world are the New York Stock Exchange (NYSE) and the NASDAQ.

• NYSE: Founded in 1792, the NYSE is famous for its physical trading floor, where traders historically shouted orders. While most trading is electronic now, a human presence remains.
• NASDAQ: This is a much younger, all-electronic market. It has no physical trading floor. Companies listed on the NASDAQ are often in the technology sector.

Two key participants make these markets work:

With thousands of companies listed on exchanges, tracking every single one would be impossible. Instead, we use stock indices to get a general sense of how the market is performing. An index is a curated collection of stocks that represents a particular segment of the market.

Think of it like a poll. You don't need to ask every person in a country their opinion to get a good idea of national sentiment. You just need a representative sample. A stock index is a sample of the market's health.

When you hear on the news that "the market was up today," the reporter is usually referring to the performance of one of these major indices. It's a simple way to summarize a very complex day of trading.

Understanding these core components—what a market is, where stocks originate, and how we measure performance—provides the foundation for learning more about investing.