The verb haber has three senses :
1. It forms perfect tenses : he hablado, has hablado, ha hablado
2. It means „there is” or „there are” :
Hay un gato en la casa – There is a cat in the house.
Hay dos gatos aquí – There are three cats here.
In this sense the form „hay” is used in the present tense.
Había dos gatos aquí – There were three cats here.
3. „Hay que” means „it is necessary”
Hay que hacerlo – It is necessary to do it.
Había que hacerlo – It was necessary to do it.
4. „Haber de” means „must” or „have to”
Has de hacerlo – You must do it.
Ella ha de escribir un relato – She must write a story.
This form is used rather only in literary language.

Haber is not used in the sense of „possessing”. To say „have” in this sense, we use the verb „tener”:
Tengo una casa grande – I have a big house.
„Tener que” means „have to” or „must”. It is a phrase , and both parts are together. Outside the phrases „tener que” and „hay que” , que means „that” or „which”.
Tengo que hacerlo – I must do it / I have to do it.