what is the difference between blackhat and whitehat?

what is the difference between blackhat and whitehat?

Hii guys I m a level 2 user.. but can anyone tell me the difference between black hat and whitehat.. n which one is good to use.. n why? Why people used these methods n for what purpose they used these methods.. I heard these words so much.. thats y I m asking this question ? Kindly give me the correct answer.. anyone rply me.. thnk u..