Sweetened condensed milk is found in a small can (14-oz.) in the baking aisle. It never goes bad, according to my knowledge, so a lot of bakers will just keep cans of it in their pantry and use it when they stumble upon one of the few recipes that calls for it. Fudge is one of those recipes. You will find this ingredient in most fudge recipes and it is what gives it that distinctive fudge-like taste.
This is also a great recipe for Holiday baking! Fudge is commonly made around this time of year, and I can see why because it is delicious and really easy to make! Plus it yields a large amount for one recipe (you can make up to 64 squares from this recipe).