Grammar
Have to
Use have to express necessity and don't /doesn't have to to express lack of necessity.
For the Present or Future
Affirmation
I have to go to the dentist today.
I have to do the washing tomorrow.
He/She has to clean the kitchen
Negative
I don't have to go to the dentist today.
I don't have to do the washing tomorrow
He/She doesn't have to clean the kitchen
For the Past
I had to go to the dentist yesterday
I didn't have to go to the dentist yesterday