Sutra ćemo složiti novi namještaj u dnevnom boravku.

It is the future tense in Croatian, specifically future I.

It is formed with:

• the present tense of htjeti (ću, ćeš, će, ćemo, ćete, će)
• • the infinitive of the main verb

So here:

• ćemo = we will
• složiti = infinitive, to put together / assemble

So ćemo složiti means we will assemble.

Because Croatian future I is normally built with the auxiliary and the infinitive as separate words:

• ja ću raditi = I will work
• mi ćemo složiti = we will assemble

So ćemo is not an ending added to the verb. It is its own word.

A useful note: Croatian has special spelling behavior when the infinitive comes first, but in your sentence the normal order is used, so they stay separate:

• Složit ćemo novi namještaj. is also possible.

This is about aspect, which is very important in Croatian.

• slagati = imperfective: ongoing, repeated, or habitual action
• složiti = perfective: a completed action, often a one-time result

In this sentence, the idea is that tomorrow we will complete the assembling of the furniture, so the perfective verb složiti is natural.

Compare:

• Sutra ćemo slagati namještaj. = Tomorrow we’ll be assembling furniture / we’ll spend time assembling it.
• Sutra ćemo složiti namještaj. = Tomorrow we’ll assemble the furniture completely.

Here složiti means something like:

• assemble
• put together
• sometimes arrange

With namještaj, it usually means assemble or put together furniture, especially new furniture that comes in parts.

In other contexts, složiti can mean different things, for example:

• složiti odjeću = fold/arrange clothes
• složiti se = agree

So the meaning depends a lot on context.

Because namještaj is the direct object of the verb, and in this sentence it is in the accusative case.

But here is the important part: namještaj is a masculine inanimate noun, and many masculine inanimate nouns have the same form in nominative and accusative.

So:

• nominative: novi namještaj
• accusative: novi namještaj

That is why the form does not visibly change.

Grammatically, namještaj is singular.

It is a collective / mass noun, similar to English furniture. Even though it refers to many pieces, Croatian treats it as singular.

So:

• novi namještaj je skup = the new furniture is expensive

If you want to talk about individual pieces, you would use other nouns, such as:

• komadi namještaja = pieces of furniture

Because this sentence describes location, not motion.

Croatian uses:

• u + locative for in/inside a place
• u + accusative for into a place, meaning movement toward it

Here, the assembling happens in the living room, so Croatian uses the locative:

• u dnevnom boravku = in the living room

Compare:

• Složili smo namještaj u dnevnom boravku. = We assembled the furniture in the living room.
• Unijeli smo namještaj u dnevni boravak. = We brought the furniture into the living room.

It is the locative singular.

The base form is:

• dnevni boravak = living room

After u meaning in, it changes to locative:

• u dnevnom boravku

Both words change:

• dnevni → dnevnom
• boravak → boravku

So this phrase is a good example of how an adjective and noun must agree in case, gender, and number.

Because Croatian often omits subject pronouns when they are already clear from the verb form.

Here, ćemo already tells you the subject is we:

• ćemo = we will

So mi is not necessary.

You could say:

• Mi ćemo složiti novi namještaj u dnevnom boravku.

But that would usually add emphasis, for example:

• We will assemble it, not someone else.

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

The original sentence:

• Sutra ćemo složiti novi namještaj u dnevnom boravku.

Other possible versions:

• Novi namještaj ćemo složiti sutra u dnevnom boravku.
• U dnevnom boravku ćemo sutra složiti novi namještaj.
• Složit ćemo novi namještaj sutra u dnevnom boravku.

The meaning stays very similar, but the focus changes.

A very important point: ćemo is a clitic, so it tends to appear near the beginning of the clause, typically in second position. That affects what word orders sound natural.

Yes. Sutra means tomorrow, and it can move depending on what you want to emphasize.

For example:

• Sutra ćemo složiti novi namještaj.
• Novi namještaj ćemo složiti sutra.
• Ćemo složiti novi namještaj sutra is not natural in standard Croatian because of clitic placement.

Putting sutra first is very common because it sets the time frame right away.

Because Croatian does not have articles like English.

So Croatian does not normally distinguish with a separate word between:

• a new furniture item
• the new furniture
• new furniture

Instead, definiteness is understood from:

• context
• word order
• demonstratives like ovaj (this) or taj (that), if needed

So novi namještaj simply means new furniture, and the exact English article depends on context.

Yes, depending on the exact meaning.

Possible alternatives include:

• sastaviti = assemble, put together
• montirati = install / assemble
• urediti = arrange, decorate

For flat-pack furniture, složiti and sastaviti are both common.
Very roughly:

• sastaviti namještaj sounds explicitly like assemble furniture from parts
• složiti namještaj can also mean that, but can sometimes feel a bit broader, like put in order / arrange / put together

In everyday speech, složiti namještaj is perfectly natural.