To tell your friends or colleagues what you have to do, use I have to…

I have to make a call.
I have to drop my kids at school.
I have to pick up my sister from college.
I have to send a parcel.
I have to send some money to my parents.
I have to buy some flowers for my wife.
I have to buy some clothes.
I have to be there before 12 o’clock.
I have to collect a parcel.

To ask what someone has to do, use Do you have to…?

Do you have to send that letter today itself?
Do you have to learn this poem by heart?
Do you have to wait for him?
Do you have to go now?
Do you have to work overtime?
To say that somebody does not have to do something, use You do not have to…
You don’t have to pay for that call.
You don’t have to wait for me.
You don’t have to bring anything.

To say that somebody has to do something, use You have to…
You have to send that parcel today itself.
You have to wait for him.
You have to be there before 8 o’clock.

To say what you have to do in a strong way, use I must…
I must finish this work today.
I must send that parcel today.
I must pay him back tomorrow.
I must get that watch fixed.
I must get a new job.
I must find out his number.