Kad prijatelji dođu na večeru, pokazat ću im mali kutak s knjigama i novi namještaj koji smo napokon složili.

Both kad and kada mean when. Kad is simply the shorter, very common form in everyday Croatian. In this sentence, kad prijatelji dođu na večeru sounds completely natural.

So:

• kad = common, everyday
• kada = also correct, sometimes a bit more formal or emphatic

There is no important meaning difference here.

After words like kad meaning when, Croatian normally uses the present tense form of a perfective verb to talk about a future event.

So:

• Kad prijatelji dođu... = When the friends come...
• not usually Kad će prijatelji doći... in this kind of time clause

This is similar to English in a way: English also says When they come, I will show them..., not When they will come...

Here, dođu is the present form of the perfective verb doći. Because it is perfective, it refers to a completed arrival in the future.

Na večeru is na + accusative.

Croatian often uses na with meals, events, and activities when someone is going or coming to them:

• doći na večeru = to come for dinner
• ići na posao = to go to work
• doći na koncert = to come to a concert

Here, večera becomes accusative singular večeru because na expresses direction or destination.

So na večeru literally means something like to dinner or for dinner.

In standard Croatian, when the future auxiliary ću comes after the infinitive, the final -i of the infinitive is usually dropped.

So:

• pokazati + ću becomes pokazat ću

This is a normal future-tense pattern:

• napravit ću
• vidjet ću
• pokazat ću

You can also say:

• Ja ću pokazati...

That version keeps the full infinitive because the auxiliary comes before it.

So both patterns are correct:

• Pokazat ću...
• Ja ću pokazati...

Croatian often leaves out subject pronouns because the verb already shows who the subject is.

Pokazat ću already means I will show because ću marks first person singular.

So ja is unnecessary unless you want emphasis:

• Pokazat ću im... = neutral
• Ja ću im pokazati... = more emphasis on I

This is very common in Croatian.

Im means to them and is the dative plural form of the pronoun oni / one / ona depending on context.

The verb pokazati often takes:

• a direct object = what is shown
• an indirect object in the dative = to whom it is shown

So:

• pokazat ću im mali kutak...
• I will show them the little corner...

Croatian does not need a separate word like to here. The dative form im already carries that meaning.

They are in the accusative because they are the direct objects of pokazat ću.

The speaker will show:

• mali kutak s knjigama
• novi namještaj

For masculine inanimate nouns, the accusative singular is often the same as the nominative singular.

So:

• mali kutak looks the same in nominative and accusative
• novi namještaj also looks the same in nominative and accusative

That is why the forms do not visibly change here.

After s meaning with, Croatian uses the instrumental case.

So:

• knjige = books
• s knjigama = with books

Here, kutak s knjigama means a little corner with books or a little book corner.

A small pronunciation/spelling note: the preposition is normally s, but it can appear as sa before certain sound combinations for easier pronunciation. Here s knjigama is normal.

Koji is the relative pronoun meaning which / that.

It refers back to novi namještaj.

In Croatian, the relative pronoun must match the noun it refers to in gender and number, and it takes the case required by its role inside the relative clause.

Here:

• namještaj is masculine singular
• inside the clause, the pronoun is the object of složili

For masculine inanimate nouns, nominative and accusative singular are the same, so the form is koji.

That is why you get:

• novi namještaj koji smo napokon složili
• the new furniture that we finally assembled

This is about Croatian clitic word order.

The auxiliary smo is a clitic, and clitics usually go in the second position of the clause or clause-like unit.

So in the relative clause:

• koji smo napokon složili

the clitic smo comes right after koji.

Croatian often prefers this kind of placement:

• koji smo već vidjeli
• koju je jučer kupila
• što sam ti rekao

You may sometimes hear different word orders in speech, but koji smo napokon složili is very standard and natural.

The verb složiti is a perfective verb with several related meanings, such as:

• to put together
• to arrange
• to assemble
• to organize

With namještaj, it most naturally means something like assembled or put together.

So:

• novi namještaj koji smo napokon složili

suggests furniture that they finally managed to assemble or set up.

The adverb napokon means finally / at last, which adds the idea that it took some time or effort.

In Croatian, namještaj is a collective singular noun, just like English furniture.

So Croatian says:

• novi namještaj = new furniture

not a plural form meaning furnitures.

Because it is grammatically singular, words agreeing with it are also singular:

• novi namještaj
• koji smo složili

Even if it refers to several physical items, the grammar treats it as singular.

The first part of the sentence is a subordinate time clause:

• Kad prijatelji dođu na večeru

Then comes the main clause:

• pokazat ću im...

In Croatian, when a subordinate clause comes before the main clause, it is normally separated by a comma.

So the comma marks the boundary between:

• When the friends come for dinner
• I will show them...

This is standard punctuation.