You can translate need with "falloir" or "avoir besoin de". So the best translations would be : - "Il nous faut un homme calme" - "Nous avons besoin d'un homme calme"

The translation "Il faut un homme calme" which is given is not the best because we don't know who need this man, there is no "nous" for the "we". This one is more the translation of "A calm man is needed", we know that there is a need : "a calm man" but we don't know who have this need.

If you want to be really precise, there is a little difference between "falloir" and "avoir besoin de". "Falloir" is stronger. If you prefer "falloir" is more "really need" and "avoir besoin de" just "need". But it's not a big difference ;)

I think because it does not directly translate as the same, it has the same meaning though

Read the tips and notes for the lesson.

https://www.duolingo.com/skill/fr/Verbs%3A-Present-1/tips-and-notes

The sentence is wrong because "de" is not needed before "besoin". But I also believe that at this particular point they are trying to teach you to use the verb "falloir" to express need of something. Read the Tips and notes for the lesson.

Yes, but in colloquial English we rarely use the passive form.