In English, we use must and have to to show obligation.
- I have to clean my room.
- You must study Japanese.
The negative forms don't have the same meaning, however. When we use must not, we mean something is forbidden. But when we use don't have to, we mean it's not required.
- You must not steal baseball cards. (It's forbidden.)
- You don't have to go to school on Sunday. (But you can.)
Technically, in the phrase have to clean, clean is an infinitive. But while students often find infinitives difficult, this kind of infinitive is not so challenging.