Using a Shampoo and conditioner bar can be tricky.  Some people can use a shampoo bar without any conditioner or vinegar rinse.  Others, like me, have hair that is dry and curly and require a vinegar rinse and a conditioner.  The vinegar rinse resets the hair and if you have hard water (like me) or dry hair (like me) a conditioner bar/conditioner and/or conditioning rinse will help nourish your hair.  

The best way to use a shampoo bar is to lather your scalp because your scalp is what gets dirty, rinse with apple cider vinegar or distilled white vinegar, then use a conditioner bar at the ends of your hair or mid-length.