Mirno sjedimo u učionici.

Mirno is an adverb. In this sentence, it describes how the action happens: we are sitting calmly/quietly.

It comes from the adjective miran meaning calm, peaceful, or quiet.
So:

• miran = calm/quiet/p peaceful
• mirno = calmly/quietly

Because it describes the verb sjedimo, Croatian uses the adverb form.

Sjediti is the infinitive, meaning to sit.

But in a full sentence, Croatian normally needs a conjugated verb, so we use sjedimo, which means we sit or we are sitting.

So:

• sjediti = to sit
• sjedimo = we sit / we are sitting

This is the same kind of difference as English to sit vs we sit.

Sjedimo is:

• 1st person plural = we
• present tense

So it literally means we sit.

In context, Croatian present tense can often mean either:

• we sit
• we are sitting

The exact English translation depends on context.

Croatian often drops subject pronouns when they are not needed, because the verb ending already shows who the subject is.

Here, the ending -mo in sjedimo tells you the subject is we.

So:

• Sjedimo = we are sitting
• Mi sjedimo = we are sitting, but with extra emphasis on we

Croatian speakers usually omit mi unless they want contrast or emphasis.

Because this sentence describes location, not movement.

In Croatian, u can mean in / into, but the case changes depending on meaning:

• u + locative = in a place, static location
• u + accusative = into a place, movement toward it

Here, the meaning is we are sitting in the classroom, so it is static location:

• u učionici = in the classroom

If you were talking about movement, you would use:

• Idemo u učionicu. = We are going into the classroom.

Učionica is the dictionary form, or nominative singular, meaning classroom.

After u with the meaning of location, the noun goes into the locative case. For many feminine nouns ending in -a, the locative singular ends in -i.

So:

• učionica = classroom
• u učionici = in the classroom

This pattern is very common with feminine nouns:

• škola → u školi
• soba → u sobi
• učionica → u učionici

Yes. This is a very common and important Croatian distinction.

• sjediti = to be sitting / to sit as a state
• sjesti = to sit down as an action of movement/change

In your sentence, sjedimo comes from sjediti, because the sentence describes the state: we are sitting.

Compare:

• Mirno sjedimo u učionici. = We are sitting quietly in the classroom.
• Sjednemo u učionici. or Sjedamo u učionici. = We sit down in the classroom.

English often uses sit for both ideas, but Croatian usually separates them more clearly.

Yes.

Croatian present tense often covers both:

• a general/habitual meaning
• an action happening now

So sjedimo could mean:

• we sit (habitually, generally)
• we are sitting (right now)

Context tells you which one is meant. In this sentence, because of mirno and u učionici, many learners will naturally understand it as we are sitting quietly in the classroom, but both readings are possible.

No, Croatian word order is fairly flexible.

Mirno sjedimo u učionici is natural and neutral, but other orders are possible depending on emphasis:

• Mirno sjedimo u učionici. = neutral, with some focus on quietly
• U učionici mirno sjedimo. = emphasizes in the classroom
• Sjedimo mirno u učionici. = also natural, with a slightly different rhythm

Even though the word order can change, the cases and verb endings still show the grammatical relationships.

A rough pronunciation guide is:

u-chi-o-ni-tsi

A few helpful sound notes:

• u = like oo in food
• č = like ch in church
• c = like ts in cats

So učionici sounds roughly like oo-CHYO-nee-tsee, though the exact rhythm depends on accent and dialect.

Putting mirno first gives it a little prominence. It highlights the manner of the action: quietly/calmly.

Croatian often places important or topical information earlier in the sentence. So starting with mirno can make the sentence feel like it is setting the scene:

• Mirno sjedimo u učionici. = Quietly, we are sitting in the classroom.

But Sjedimo mirno u učionici is also correct and natural. The difference is mainly one of emphasis and style, not basic grammar.