Zebra stoji pokraj žirafe u zoološkom vrtu.

Because pokraj normally requires the genitive case.

The base form is žirafa = giraffe.
In the genitive singular, it becomes žirafe.

So:

• žirafa = nominative, the basic dictionary form
• pokraj žirafe = next to / beside the giraffe

This is very common in Croatian: certain prepositions force a specific case, and pokraj is one of them.

Because u here means in, describing location, so it takes the locative case.

The basic phrase is:

• zoološki vrt = zoo

In the locative singular, it becomes:

• u zoološkom vrtu = in the zoo

Both words change because the adjective must agree with the noun:

• zoološki → zoološkom
• vrt → vrtu

So this is a good example of adjective-noun agreement in case, number, and gender.

Stoji comes from stajati, which basically means to stand.

In this sentence, it can mean:

• is standing
• sometimes more loosely is positioned or is located

So Zebra stoji pokraj žirafe... most naturally means The zebra is standing next to the giraffe...

Croatian often uses stajati where English might sometimes prefer be if the idea is physical position.

Yes, zebra is a feminine noun in Croatian.

Many feminine nouns end in -a, and zebra follows that pattern:

• nominative singular: zebra
• genitive singular: zebre
• dative/locative singular: zebri
• accusative singular: zebru

In this sentence, zebra is the subject, so it stays in the nominative: Zebra stoji...

Because Croatian has no articles like English a/an/the.

So:

• zebra can mean a zebra or the zebra
• žirafe can mean a giraffe's / of the giraffe, depending on context
• u zoološkom vrtu can mean in a zoo or in the zoo

Context tells you which meaning is intended.
That is normal in Croatian and other Slavic languages.

Yes, Croatian word order is more flexible than English because case endings show the grammatical relationships.

The neutral order here is:

• Zebra stoji pokraj žirafe u zoološkom vrtu.

But you could also hear variations like:

• U zoološkom vrtu zebra stoji pokraj žirafe.
• Pokraj žirafe stoji zebra.

These versions shift emphasis a little:

• starting with u zoološkom vrtu emphasizes the location
• starting with pokraj žirafe emphasizes what the zebra is next to

English is much stricter about word order, so this often feels new to learners.

All three can mean next to / beside / by, and in many contexts they are very similar.

• pokraj žirafe = next to the giraffe
• pored žirafe = next to the giraffe
• kraj žirafe = by the giraffe

A few notes:

• pored is very common in everyday speech
• pokraj can sound a bit more formal or literary in some contexts
• kraj is also common, but in some contexts it can feel slightly stylistic or regional

For a learner, it is useful to know that all of them normally take the genitive.

A rough guide:

• ž sounds like the s in measure
• žirafe ≈ zhi-RA-fe
• zoološkom ≈ zo-o-LOSH-kom

A few useful sound notes:

• ž = voiced sh sound
• š = plain sh
• Croatian pronunciation is usually quite regular, so words are mostly pronounced as written

Also:

• vrtu may look strange to English speakers because of the consonant cluster vrt
• Croatian allows clusters like this much more easily than English does

Because u is the normal preposition for being in an enclosed or defined place like a zoo, city, room, school, or park in many contexts.

So:

• u zoološkom vrtu = in the zoo

Croatian often distinguishes location with prepositions like:

• u = in
• na = on / at, depending on the place

For example:

• u gradu = in the city
• na stolu = on the table
• na poslu = at work

You cannot choose freely between u and na; each noun tends to go with one or the other depending on normal usage.

Yes. Stoji is present tense, 3rd person singular.

From stajati:

• ja stojim = I stand / I am standing
• ti stojiš = you stand
• on/ona/ono stoji = he/she/it stands

Since zebra is singular, the verb is singular too:

• Zebra stoji = The zebra stands / is standing

Yes, sometimes.

In a very literal sense, stoji means is standing.
But in real usage, Croatian can use stajati for position or placement, especially when describing where something or someone is.

So depending on context, the sentence may suggest:

• the zebra is physically standing next to the giraffe
• the zebra is positioned next to the giraffe

With animals, the most natural first interpretation is still the literal one: the zebra is standing next to the giraffe in the zoo.