Kind of a loaded question but I will give it my best shot.
Futures prices are determined on the Chicago Board of Trade and Chicago Mercantile Exchange. Crop and livestock producers / crop and livestock buyers buy and sell contracts of the commodities through the exchange. Local prices are determined by local market factors. The difference between the local price at the elevator and the price on the board of trade is called basis. Basis is impacted by local supply/demand factors, access to export markets, local end users, etc.
I can get into more detail if you want but it's hard to know where to start and stop. Iowa State has one of the best marketing professors/extension agents in the country IMO in Chad Hart. He teaches a marketing class at ISU that's really good - lecture notes are in powerpoint presentations on this page if you or anyone is interested in learning more:
:
http://www2.econ.iastate.edu/faculty/hart/Classes/econ337/Spring2016/index.htm