U novom kvartu postoji mala trgovina u kojoj kupujem svježi špinat i poriluk.

Because u here means in, and when u expresses location, it takes the locative case.

• kvart = neighborhood, district
• u kvartu = in the neighborhood
• novom is the locative singular form of novi and agrees with kvartu

So:

• u novom kvartu = in the new neighborhood

If u meant movement into something, Croatian would usually use the accusative instead.

Kvart usually means neighborhood, city district, or part of town. It is a very common everyday word.

So u novom kvartu is something like:

• in the new neighborhood
• in the new district

It is less formal and more everyday than some other location words.

Yes, Croatian can often use either postoji or ima for existence, but they are not exactly the same in tone.

• postoji = exists / there is
• ima = there is / there are / has, depending on context

In this sentence, postoji mala trgovina sounds a bit more neutral or slightly more formal, like there exists a small shop.

A speaker could also say something like U novom kvartu ima jedna mala trgovina, especially in everyday speech.

So the difference is mostly about style and nuance:

• postoji = emphasizes existence
• ima = very common conversational way to say there is

Because it is the subject of the verb postoji.

The structure is basically:

• postoji = there exists / there is
• mala trgovina = a small shop

Since trgovina is the thing that exists, it stays in the nominative singular:

• trgovina = shop
• mala trgovina = small shop

Also notice the adjective agreement:

• mala is feminine singular nominative
• it matches trgovina, which is feminine singular

U kojoj means in which, and in natural English it is usually translated simply as where.

It refers back to trgovina:

• trgovina = shop
• u kojoj kupujem... = in which I buy... / where I buy...

Why kojoj?

Because it comes from the relative pronoun koji, which changes form depending on:

• gender
• number
• case

Here it refers to trgovina, which is:

• feminine
• singular

And because it follows u in a location meaning, it must be in the locative.

So:

• koja = basic feminine form
• kojoj = feminine singular locative/dative form

Here it is locative because of u.

Yes, very often you can.

So these are both possible:

• trgovina u kojoj kupujem...
• trgovina gdje kupujem...

The version with u kojoj is a bit more explicitly grammatical and can sound more formal or careful.
The version with gdje is very common in everyday speech.

So:

• u kojoj = more literally in which
• gdje = where

Both are useful to know.

Because kupujem is the imperfective verb form, which is the normal choice for a repeated, habitual, or ongoing action.

Here the meaning is something like:

• where I buy
• where I usually buy
• where I shop for

So Croatian uses:

• kupovati / kupujem = imperfective, ongoing or habitual buying
• kupiti / kupim = perfective, a completed act of buying

In this sentence, the speaker is not talking about one single completed purchase. They are describing a regular place where they buy things. That is why kupujem fits naturally.

They are in the accusative, because they are the direct objects of kupujem.

The speaker buys:

• špinat
• poriluk

So they are the things being bought.

However, both špinat and poriluk are masculine inanimate nouns, and in Croatian the accusative singular of masculine inanimate nouns is usually the same as the nominative singular.

That is why you see:

• špinat
• poriluk

with no visible change.

Because svježi must agree with špinat in case, gender, and number.

Here špinat is:

• masculine
• singular
• accusative (but masculine inanimate accusative looks like nominative)

So the adjective takes the corresponding form:

• svježi špinat = fresh spinach

This ending may feel surprising at first, but it is just the normal agreement pattern.

Strictly speaking, svježi directly agrees with špinat, the first noun.

So grammatically you have:

• svježi špinat
• i poriluk

In practice, many speakers will understand the freshness as applying naturally to both items from context, especially in a shopping sentence. But the adjective itself is only stated once.

If you wanted to make it fully explicit for both nouns, you could repeat it:

• svježi špinat i svježi poriluk

Croatian often avoids repetition when the meaning is already clear.

Because Croatian does not have articles like English.

So trgovina can mean:

• a shop
• the shop

depending on context.

The same is true for many nouns in the sentence. English has to choose between a and the, but Croatian usually leaves that information to context, word order, or extra words if needed.

That is why mala trgovina can be translated as a small shop here, even though there is no separate word for a.

No, Croatian word order is fairly flexible, but some orders sound more natural than others depending on focus.

This sentence begins with the location:

• U novom kvartu...

That sets the scene first: in the new neighborhood.

Then comes:

• postoji mala trgovina

This is a natural way to introduce something new: there is a small shop.

Then the relative clause:

• u kojoj kupujem...

comes right after trgovina, because it describes that noun.

So the sentence is well organized as:

1. place
2. existence of something
3. description of that thing

Other word orders are possible, but this one is very natural and clear.