will have (obligation)
I will have to hire a car to go to the meeting
He will have to work harder if he wants to pass his exam
If you are ill, you will have to call a doctor.
Mary is ill. She will have to stay in bed for some days
be able to (possibilité)
He will be able to repair the car, he is a mechanic
I will be able to go with you, I have finished my homework
I will be able to make this cake for your birthday
