have to + a verb means you need to do it. It is a rule, or you have no choice.
have to + a verb
I have to be at school at eight.
We have to wear a uniform at work.
Not "I have be at school at eight." — say "I have to be at school at eight.". Say have to, with to, before the verb.
Try it: Amina: Can I leave these boxes in the hall? Lars: No. The landlord checks the halls every week. We ___ keep them in our apartments. Choose what Lars says. (have / have to / don't have to) Answer: have to — The landlord checks the halls, so keeping the boxes inside is not a choice: Lars says have to + keep. have alone is missing to, and don't have to would make it a choice.
he, she, it: has to
With he, she and it, say has to.
He has to leave at seven.
The doctor has to see ten people today.
Not "He have to leave at seven." — say "He has to leave at seven.". With he, she and it, say has to.
Try it: Amina: Why is the man in 2B so busy? Lars: He ___ move out on Friday. Choose what Lars says. (have to / has / has to) Answer: has to — With he, say has to + move. have to goes with I, you, we and they, and has alone is missing to.
don't have to + a verb
don't have to + a verb means it is not a rule. You can do it, or not.
You don't have to call me. I'm fine.
We don't have to cook tonight.
Try it: Amina: The library closes at eight. Is my book late? Lars: No. You ___ take it back today. You have two weeks. Choose what Lars says. (don't have to / have to / doesn't have to) Answer: don't have to — Amina has two weeks, so taking the book back today is her choice: don't have to + take. have to would mean today is the last day, and doesn't have to goes with he, she and it, not you.
he, she, it: doesn't have to
With he, she and it, say doesn't have to.
She doesn't have to wear a uniform.
He doesn't have to work on Friday.
Not "She don't have to go." — say "She doesn't have to go.". With he, she and it, say doesn't have to.
Try it: Amina: Does your friend go to a classroom for her English class? Lars: No. She ___ go. The class is online. Choose what Lars says. (don't have to / doesn't have to / has to) Answer: doesn't have to — The class is online, so going to a classroom is not needed, and with she you say doesn't have to. don't have to goes with I, you, we and they, and has to would send her to the classroom.
Do you have to? Does he have to?
To ask about a rule, say Do you have to + a verb? With he, she and it, say Does he have to + a verb?
Do I have to buy a ticket? Yes, you do.
Does she have to study tonight? No, she doesn't.
Not "Does he has to go?" — say "Does he have to go?". After does, say have to, not has to.
Try it: Amina: ___ I have to take off my shoes? Lars: Yes, please. The floor is new. Choose Amina's first word. (Does / Am / Do) Answer: Do — With I, a question about a rule starts with Do: Do I have to take them off? Does goes with he, she and it, and Am does not go with have to.
A rule, or a choice
Do you need to do it? Say have to. Can you choose? Say don't have to.
At this school, you have to wear a uniform.
You don't have to wear a tie, but you can.
Try it: Amina: Can I go home now? Lars: Sure. You ___ stay. We can do it tomorrow. Choose what Lars says. (have to / don't have to / has to) Answer: don't have to — They can do it tomorrow, so staying is Amina's choice: don't have to + stay. have to would keep her there tonight, and has to goes with he, she and it.