Have is a helping verb and is generally used with the pronouns I / You / We / They and plural nouns. It is used in present tense. It's past form is 'had'.
Has is used with the prounouns He / She / It /any name / who and singular nouns. However, there are some exceptions which will be explained later on in the lesson. In general, has is a helping herb in present form and it's past form is also 'had'.