The verb Have is used in two ways.

1. As a Transitive verb to mean concrete or abstract sense of possession.

You have a fine car.

This rose tree has white flowers.

I have much work to do.

He has a sore throat.

2. As an Auxiliary Verb.

With the perfect participle of another verb, it forms two more tenses.

(a) The Present Perfect.

I have read this book twice.

(b) The Past Perfect.

You had been there before, hadn’t you?

Have and Had followed by the Infinitive form a common way of expressing obligation or fulfilment (fulfillment) of a promise.

I have to be at school before nine.

Don’t forget that you have to write to your aunt tomorrow.

When have we to be at the station?