Learn Hardcore Portuguese (Brazil): É importante que você fique tranquilo durante a prova. - It is important that you stay calm during the test.

In Portuguese, expressions like É importante, É necessário, É bom, É melhor, É fundamental often introduce a clause with que meaning that:

É importante que… = It’s important that…
So que is the connector that links the impersonal evaluation (it’s important) to the action you want someone to do.

Why is the verb fique and not fica?

Because É importante que… typically triggers the present subjunctive in Brazilian Portuguese when you’re expressing a recommendation, necessity, or importance.

(que) você fique = present subjunctive of ficar for você
Indicative (você fica) would sound like you’re stating a fact/habit: you stay/you end up (as a description), not advising or emphasizing what should happen.

How do I know fique is subjunctive, and what is the infinitive?

The infinitive is ficar (to stay / to become).
Present subjunctive of ficar:

que eu fique
que você fique
que ele/ela fique
que nós fiquemos
que vocês fiquem
que eles/elas fiquem

So fique matches você (and also eu/ele/ela in form, but the subject here is você).

What does ficar tranquilo mean compared to estar tranquilo?

Both can translate as to be calm, but the nuance differs:

ficar tranquilo often means to become calm or to stay/keep calm (a change or an instruction to maintain calm).
estar tranquilo is more simply to be calm (describing a state).

In advice contexts, ficar tranquilo is very common: (It’s important that) you stay calm.

Why does it say você instead of tu?

In most of Brazil, você is the default informal/neutral you, and it takes 3rd-person verb forms (like você fique).
In regions where tu is common, you might hear:

É importante que tu fiques tranquilo durante a prova.
But many Brazilians who say tu still use 3rd-person verbs informally (tu fica), depending on the region.

Does tranquilo agree with the person? What if I’m speaking to a woman or to more than one person?

Yes—adjectives agree in gender and number:

to a man: você fique tranquilo
to a woman: você fique tranquila
to a group (mixed/men): vocês fiquem tranquilos
to a group (all women): vocês fiquem tranquilas

Why is durante a prova and not durante prova?

Portuguese usually needs an article where English can omit it. Here, a prova means the exam/test (a specific event).
So durante a prova = during the exam.
Without the article, it would sound incomplete or unnatural in most contexts.

Can I also say na prova instead of durante a prova?

Often, yes, but the meaning shifts slightly:

durante a prova = during the exam (focus on the time period while it’s happening)
na prova = in the exam / on the test (can mean during it, but can also lean toward the setting or the context of the exam)

Both are common; durante is more explicitly about time.

What does É importante literally mean, and why is there no subject?

It’s an impersonal structure:

É importante… = It is important…

Portuguese often uses ser + adjective impersonally without an explicit subject, similar to English it is…. The it is understood.

Where does the stress/pronunciation fall in key words?

Common stress points:

importante: im-por-TAN-chi (final e often sounds like i in Brazil)
você: vo-SÊ (the ê is stressed)
fique: FI-ki (the que sounds like ki)
tranquilo: tran-QUI-lo
durante: du-RAN-chi
prova: PRO-va

Is the word order flexible? Could I move parts around?

Some flexibility is possible, but the given order is the most natural:

É importante que você fique tranquilo durante a prova.

You could move the time phrase for emphasis:

É importante que você fique tranquilo, durante a prova. But too much rearranging can sound marked or less smooth. The core pattern É importante que + subjunctive is usually kept intact.

Are there other natural alternatives that mean the same thing in Brazilian Portuguese?

Yes—common variations include:

É importante você ficar tranquilo durante a prova. (very common in speech; many Brazilians use infinitive here)
É essencial que você mantenha a calma durante a prova. (more formal; mantenha is subjunctive of manter)
É bom que você fique tranquilo durante a prova. (a bit softer than importante)