Futures are contracts between two parties who agree to exchange some asset for a predetermined price at a date set in the future. Futures are highly products which carry very large (up to hundreds of thousands of dollars per contract). They are not meant for small account sizes.
Futures markets are divided into six sectors: Equities (the stock market), energy, metals, (which inversely track rates), agriculture, and currencies (foreign exchanges aka "forex"). Within these sectors are several different products that can be traded such as gold and silver in the metals sector, or oil and natural gas in the energy sector.