Have is used to make the present perfect tense (it is always followed by the past participle).
Has is used for the third person singular.
Had is used for past tenses especially the past perfect tense. It describes an action that began in the past and continues into the present or that occurred in the recent past.
In statements
I have a dog.
You have something on your shirt.
We have seen it before.
They have called me three times.
He/she has lived in America.