where to use had and hadn't

had is used in positive sense.. and hadn't is used in negative sense... had is a past perfect tense.. we use had in a sentence when we are talking about something which is finished in past long time before but we are now talking about it's impact.

"Had" is used in past perfect tense as a helping verb and also to show past possession. For ex:- He had done his work. She had a watch. "Hadn't" is used in only past perfect tense as a helping verb to make a sentence negative. For ex:- He hadn't done his work.