The price of the commodity is subject to supply and demand factors. Risk is actually the reason exchange trading of the basic agricultural products began. For example, a farmer risks the cost of producing a product ready for market at sometime in the future because he doesn't know what the selling price will be. A speculator can pay the farmer or anyone else producing commodities because the speculator wants to make a profit. This is called trading in futures.
Options are one type of derivative, because their value derives from the value of the underlier.
For stock options, the amount is usually 100 shares. Not every stock has options associated with it, but a lot of them do. Each option contract has a specific symbol. This list of options symbols is called an option chain. Our Futures, Options, and Commodities Quotes page links to sites that let you check the quotes on options using these ticker symbols.