Dopamine reward system is a part of the human brain that rewards or gives a feel good feedback by releasing neurons called a neurotransmitter.
Please note that your question is not specific and thus i would give you a general overview that should help you get to the right answer.
This is better explained by giving an example. Let us say that a person eats a sweet bar of chocolate, then dopamine is released from the brain and this reinforces the behavior.
That is why when a person does something fun or eats something sweet, he wants to eat another or do perform that behavior again.
