Break them up and place them in a food processor. Chop until you have fine crumbs, as well as some small and medium sized pieces. You want about 1 cup worth.
If you can't find the 10 oz container of sweetened condensed milk, use a 14 oz. I don't recommend using it all, the way some recipes do, as I find it really sweet.
Don't try and do this low fat, the best of ingredients are needed when so few are being used in the ice cream.