If you don't have buttermilk on hand I suggest you use a different recipe known to work with the ingredients you have. In a pinch, lemon juice, lime juice, or vinegar can be added to regular milk. The acid in vinegar or the citrus juice sours the milk and works as the leavening with the baking powder and soda. Stir the milk and vinegar/juice together and allow it to sit a few minutes before adding it to the dry ingredients. But know the formula. I recommend Buttermilk if you want killer biscuits. But I often use a concoction of regular milk, sour cream, feta cheese and lemon juice in place of buttermilk. It depends on what is in the fridge. Start experimenting after you master getting fluffy biscuits that raise well.