What is the difference between a positive and a negative sanction?

Positive sanctions (or rewards) are pleasant things we can do to try to make people conform and behave in a routine, predictable, fashion. An example is buying a child an ice cream to make it stop crying.

Negative sanctions (or punishments) are basically the not very nice things we can do to try to make people conform and behave, such as hitting someone or withholding food.