Any retail investor can now trade in commodity markets. This group of assets serves to diversify one's investment portfolio. Commodity prices usually move opposite to stock prices, so commodities work as protective assets during stock market crises.
Commodity prices vary based on a current market demand/supply model. A war in a country where much gold is produced will increase gold prices as the supply will fall. Conversely, an increase in oil production in the Middle East will drop oil prices due to a larger supply. Commodities protect investors against inflation.