Moramo izaći iz autobusa kod škole.

Moramo is the 1st person plural present tense of morati = to have to / must.

So:

• moram = I must
• moraš = you must
• mora = he/she/it must
• moramo = we must

Croatian usually drops subject pronouns when they are not needed, because the verb ending already shows who the subject is. So moramo already means we must.

You could say Mi moramo, but that adds emphasis, like We must.

After modal verbs like morati (must / have to), Croatian normally uses the infinitive of the main verb.

So the structure is:

• moramo = we must
• izaći = get out / go out

Together: moramo izaći = we must get out

This is similar to English must leave, must go, must get out, where must is followed by the base form of the verb.

This is a question of aspect, which is very important in Croatian.

• izaći = perfective
• izlaziti = imperfective

Here, izaći is used because the sentence is about one complete action: getting off the bus at a particular place.

Compare:

• Moramo izaći iz autobusa kod škole.
  = We need to get off the bus by the school.
  (one completed event)

• Svaki dan izlazimo iz autobusa kod škole.
  = Every day we get off the bus by the school.
  (repeated/habitual action)

So izaći fits this sentence better.

Because the preposition iz means out of / from, and after iz, Croatian uses the genitive case.

So:

• dictionary form: autobus
• after iz: autobusa

That is why the sentence has:

• iz autobusa = out of the bus / off the bus

This is a very common pattern:

• iz kuće = out of the house
• iz škole = out of the school
• iz auta = out of the car

Because kod also requires the genitive case.

So:

• dictionary form: škola
• after kod: škole

That gives:

• kod škole = by the school / near the school

So both nouns in the sentence change because both are controlled by prepositions:

• iz autobusa
• kod škole

Kod škole usually means by the school, near the school, or at the school in the sense of in the area of the school / next to it.

It does not usually mean inside the school building.

That is an important contrast:

• kod škole = by/near the school
• u školi = in the school

So this sentence means you need to get off the bus by the school, probably using the school as a landmark.

Yes, they are related, but they do different jobs.

• izaći tells you the action: to go out / get out
• iz autobusa tells you out of what

So:

• izaći = get out
• iz autobusa = out of the bus

This is not strange in Croatian; it works much like English:

• get out of the bus
• come out of the house

The verb gives the action, and the prepositional phrase gives the source/place.

Yes. Croatian word order is fairly flexible, although some orders sound more natural than others depending on emphasis.

The neutral order here is:

• Moramo izaći iz autobusa kod škole.

But you could also say:

• Kod škole moramo izaći iz autobusa.
  This emphasizes where you need to get off.

The original version is probably the most natural if you are just giving straightforward information.

Yes, that is grammatically correct.

But mi is usually unnecessary, because moramo already shows we.

Use mi only if you want emphasis or contrast, for example:

• Mi moramo izaći kod škole, a oni kod muzeja.
  = We have to get off by the school, and they by the museum.

So in most normal situations, Moramo by itself is enough.

Usually it can mean either must or have to, depending on context.

• Moramo izaći iz autobusa kod škole.
  could be understood as
  We must get off the bus by the school
  or
  We have to get off the bus by the school

In everyday speech, morati often covers both ideas. The exact English translation depends more on context and tone than on Croatian grammar alone.