"musn't" (Must not) del verbo - must . es deber en español. Puedes utlilizar esta palabra cuando, algo tiene que ser hecho, por ejemplo - He must fill the bottle of water/debe llenar la botella de ague . / we must not let anyone pass/nosotros no debemos permitir que nadie pase. has to y doesnt have to (does not have to) es como el verbo (tener) por ejemplo. "He has to drink the water"/tiene que beber el agua" tambien "does not have to" solo es la forma negativa. por ejemplo - "I don't have to wake up early" / "No tengo que despertar temprano" ESPERO QUE ESTO AYUDE

Verb contractions are very common in the English language. Examples: doesn't, can't, won't, shouldn't, didn't, plus many more. Mustn't is pronounced musn't but English dictionaries make reference to the spelling as mustn't. I am Canadian and will comment that mustn't is basically an obsolete word in my country. As in any language, the use of verbs in English are a daily part of life. Verb contractions are a daily part of English conversations. For example, "you didn't (did not) call me... I couldn't (could not) because my cell phone wasn't (was not) working." "I can't (cannot) forget to study for the exam." English verb contractions are used during informal conversations in all interactive settings, especially among family and friends, but in the community too. Of course, there are a few cautions to consider. In formal writings, such as a student submitting university essays, verb contractions are not preferred and often corrected by many of the professors. Also, in the writing of legal documents for court proceedings and when a lawyer answers a judge in the courtroom, verb contractions are avoided. You would not use contractions on a curriculum vitae (resume) needed for a job application.

In America no one has said musn't for hundreds of years

Eu sou do barril mais falo inglês

I don't know when I can use mustn't or doesn't in sentences