why do we have the food stamp program?

Dear Luribe, 

The Food Stamp Program in the United States provides food to low
income people. Its advantages are the fact that the needy, on the one
hand, get their basic needs - food - and thus contibutes to the
prevention of malnutrition and hunger.

You can read more about the programme at: 
Wikipedia, "Food Stamp Program"
<http://en.wikipedia.org/wiki/Foodstamps> 

Further Links: 

Food Stamp Program
<http://www.fns.usda.gov/fsp/> 

Federal Food Program
<http://www.frac.org/html/federal_food_programs/programs/fsp.html> 

I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it.

Note it is run by the USDA (Department of Agriculture). The goverment
has a strong motivation to subsidize farmers In order to keep crop
surpluses from crushing prices as happened during the Depression.
(Picture milk poured on the road because there was too much of it.)

Food stamps are only one way for the goverment to get rid off food it
is forced to buy when it subsidizes various crops.