Has is used when we are talking about singular number. Eg. He has, she has, it has been.
However, there are some exceptions while we are using has. Eg. In case of ‘I’ and ‘you’, although may indicate singular number, we have to use have. So we will say I have , not I has. Then we will say you have, but not you has.
Have is used for most pleural forms and as the examples above. Eg. We have, they have.