I understand the basic concept behind investing in a company via stock purchases: you get some minuscule percentage of the company, and get to benefit from that ownership.
Investing in commodities (eg corn, oil, etc) seems to be quote different - as they are done on a per-contract basis (November soybeans, for example).
How do they actually vary, and what happens if I buy a November soybeans contract today (May)? Do I have to sell it in November because it will have come due? Or do I hold onto it as long as I want it (like i would with a stock), or is it something else entirely?