A jerky gun is used for making strips of meat jerky from ground meats.
It consists of a tube, with a press, and interchangeable tips: a flat tip for strips of jerky, a round tip for sticks.
To use, you mix ground meat with some spices (either your own mix, or a purchased packet, such as those from American Harvester, which includes a cure for the meat as well), and put the meat mixture into the jerky gun. You then press it to to extrude the meat, and then dry the strips in a food dehydrator.
Some sources advise that when making your own spice mix, you should consider including a cure such as Prague Powder #1 to help prevent the growth of C. botulinum (which causes botulism, often fatal) in the meat.
They also feel that if you are making jerky out of beef ground at supermarkets (as opposed to at home), nothing may make it safe, because the food hydrator may not achieve temperatures high enough to eliminate the risk of any E. coli.
See the National Center for Home Food Preservation’s site for safe, lab-tested directions on making jerky.