Present Tense must, have to
probably Je dois étudier.
Il doit être malade. I must (have to) study.
He's probably sick.
Passé Composé had to (and did),
must have Il a dû partir. He had to leave.
Imperfect was supposed to,
used to have to Elle devait chanter ce soir. She was supposed to sing tonight.
Future will have to Tu devras payer l'argent. You will have to pay money.
Conditional should Vous devriez manger les fruits. You should eat fruits.
Past Conditional should have Ils auraient dû jouer. They should have played.
In the present tense, you can also express I am supposed to with Je suis censé + infinitive. To express you don't have to instead of you must not, use vous n’êtes pas obligé de instead of vous ne devez pas or il ne faut pas.