Prenesi fotelju stepeništem.

Prenesi is the imperative singular form of the verb preneti / prenijeti, meaning to carry/transfer from one place to another.

So Prenesi fotelju stepeništem. means something like Carry the armchair via the stairs / up or down the stairs.

Because it is imperative singular, the speaker is telling one person to do it.

Fotelju is in the accusative singular, because it is the direct object of the verb prenesi.

• nominative: fotelja = an armchair
• accusative: fotelju = the armchair / an armchair as the thing being carried

This is very common in Serbian: the thing directly affected by the action usually goes into the accusative.

Stepeništem is instrumental singular of stepenište (staircase / stairway).

Here the instrumental is used to express the route, means, or path by which something is moved. So stepeništem means:

• by the stairs
• via the staircase
• using the staircase route

This is a normal use of the instrumental in Serbian, especially with movement.

In Serbian, the instrumental case can sometimes be used without a preposition to show the path or means.

So:

• Prenesi fotelju stepeništem. = Carry the armchair by way of the stairs.

English usually needs something explicit like up the stairs, down the stairs, through the stairwell, or via the staircase, but Serbian can express that idea just with the instrumental form.

Not by itself. Stepeništem only tells you that the movement happens via the staircase. It does not specify direction.

So the sentence could mean:

• carry it up the stairs
• carry it down the stairs
• carry it through the stairwell

The exact direction depends on context.

This is an aspect question.

• nositi = to carry, often in a more general, repeated, or ongoing sense
• preneti / prenijeti = to carry over / move from one place to another, usually with a sense of completion

In Prenesi fotelju stepeništem, the speaker wants a completed action: move the armchair from one place to another. That is why a perfective verb is used.

Prenesi comes from the perfective verb preneti / prenijeti.

Perfective verbs in Serbian often focus on the action as a whole completed event. That fits commands like this very well:

• Prenesi fotelju = Move/carry the armchair over (get it done)

An imperfective command would sound different and would usually emphasize process, repetition, or ongoing action rather than a single completed result.

Yes. Serbian word order is more flexible than English word order.

For example, these are possible:

• Prenesi fotelju stepeništem.
• Fotelju prenesi stepeništem.
• Stepeništem prenesi fotelju.

The basic meaning stays similar, but the emphasis changes:

• starting with Prenesi sounds like a straightforward command
• starting with Fotelju emphasizes the armchair
• starting with Stepeništem emphasizes the route

The version you were given is a very natural neutral command.

Not exactly. Fotelja usually means an armchair or easy chair, not just any chair.

A general chair is usually stolica.

So:

• stolica = chair
• fotelja = armchair

That is why the sentence is specifically about an armchair, which also makes sense because it is the kind of thing people might have trouble moving up or down stairs.

A rough English-friendly guide is:

PREH-neh-see FOH-teh-lyoo steh-peh-NEESH-tem

A few pronunciation notes:

• j in Serbian sounds like English y
• š sounds like English sh
• stress is not usually marked in normal writing, but this approximation will help you say it understandably

So:

• fotelju sounds roughly like fo-TE-lyu
• stepeništem includes niš, which sounds like neesh

By itself, it is a plain imperative, so it can sound:

• neutral
• direct
• efficient
• or a bit abrupt, depending on tone and situation

If you want to make it softer or more polite, Serbian often adds words such as:

• Molim te, prenesi fotelju stepeništem. = Please carry the armchair via the stairs.
• Možeš li da preneseš fotelju stepeništem? = Can you carry the armchair via the stairs?

So the original is not automatically rude, but it is definitely a direct command.

Yes, it is grammatical and natural, but in real life many speakers might choose a slightly more specific version depending on context, for example:

• Prenesi fotelju uz stepenice. = Carry the armchair up the stairs.
• Prenesi fotelju niz stepenice. = Carry the armchair down the stairs.

Your sentence is still perfectly normal; it just leaves the direction unspecified and focuses on the staircase as the route.