Some of the various types of sausage
Fresh sausage- Exactly what it says - fresh meat ground and seasoned and stuffed into a casing so that there are no air pockets. Usually the meat is ground with a 3/16" (4.5mm) to 1/4" (6 mm) Plate. It may be served in small casings for breakfast links or in larger casings for full size sausages. It can also be sliced and cooked without the casing as breakfast patties. Shelf life for fresh sausage is very short. It must be refrigerated to be kept 2 or 3 days or frozen to be kept longer. Quality deteriorates rapidly but boy, is it good when it's fresh!
Smoked Sausage - This is fresh sausage that has been smoked. A salt cure is added to control botulism during the smoking process (and storage). Salt cure or curing salt is 6.25% sodium nitrate mixed with 93.75% salt and dyed pink as a tattletale. Another name for this product is Prague powder or Instacure. One ounce will cure 25 lbs of meat when mixed thoroughly. Smoking and the cure also lengthen the shelf life when the sausage is refrigerated.
Dried sausage - Smoked sausage that has been smoked or dehydrated until most of the moisture has been removed. This is a great snack and is very similar to jerky but it can be made with ground trimmings rather than long strips of meat. Since the casing can be stripped off, it is cleaner than a pocketful of jerky. It most certainly must have curing salt but it will keep even without refrigeration. (at least for a while - mold will eventually show up.) Refrigeration still extends shelf life.
Summer Sausage - A basic summer sausage (there are many varieties) is a sausage that is smoked or slowly heated to a temperature of approximately 155 degrees fahrenheit (any higher and the fat turns to oil and the sausage is a cooked sausage) for a period of time and then refrigerated for a period of time to age it. This adds a tartness to the flavor. If you are in a hurry, encapsulated citric acid can be added for tartness.) It is then stuffed into a fibrous casing which resembles paper and is usually 2" or 3" in diameter.
There are many more varieties but
those are by far the most popular and simplest to produce.
One of the most complete sources of the items that you will need to make sausage can be found at the link to Heinsohn's Country Store.