I don't recommend you to talk to him right now. He's very stressed. (SHOULD)
You shouldn't talk to him right now. He's very stressed.
At the cinema, you have the obligation to stay in silence, so everybody can pay attention to the film. (MUST)
At the cinema, you must stay in silence, so everybody can pay attention to the film.
He is not obligated to take the extra test, but it would certainly help him a lot. (HAVE TO)
He doen't have to take the extra test, but it would certainly help him a lot.
It's not possible for her to talk to you right now. Can you call back in 10 minutes? (CAN)
She can't talk to you right now. Can you call back in 10 minutes?
