A stock index is a single number that summarizes the price action of a basket of companies. The S&P 500 tracks roughly 500 large US firms, the Nasdaq-100 tracks the 100 largest non-financial names on the Nasdaq exchange, and the Dow Jones Industrial Average follows 30 blue-chip stocks.
A CFD is a contract between you and your broker to exchange the difference in an asset's price from when you open the trade to when you close it. You never own the underlying asset. That single distinction shapes everything about how CFDs work, what they cost, and why regulators treat them differently from traditional investing.
Leverage lets you control a larger position than your account balance would normally allow. A $10,000 account with 10:1 leverage can open a $100,000 position. That sounds powerful, and it is — in both directions.
People have been trading oil, gold, wheat, and cattle for centuries. What has changed is how you access these markets. You no longer need a seat on the Chicago Mercantile Exchange or a warehouse full of soybeans.