Had is the Past form of have and has,it is used with all Pronouns and we use it to talk about past things,For example,i had a bad dream last night.
in addition to this the verb had is utilized to shape the past perfect tense , so you should utilize the past tense of the verb "to have," which is had when you want to form the past perfect tense, and add it to the past participle of the fundamental verb. For instance: subject + had + past participle = past perfect tense.