You can eat the stalks any time, but it is best to wait until they are pretty thick and fleshy.  They will not always turn red, but if they do that can guide you as well.  You can make loads of things, although pie is certainly a favorite.  Cobbler too, usually with other berries.  You can stew it into a sweet sauce for topping pancakes or cakes or shortbread.  You can also cook it with meats or fish.