Learn Hardcore Croatian: U sredini stola stoji velika zdjela, a oko ruba stola su tanjuri. - In the middle of the table there is a big bowl, and around the edge of the table there are plates.

sredini – locative singular of sredina (middle).
- The preposition u (in) uses the locative when it expresses a static location (in/at somewhere).
stola – genitive singular of stol (table).
- The noun sredina (middle) often takes the genitive to show of what: sredina stola = the middle of the table.

So literally: u sredini stola = in the middle of the table (locative + genitive).

Could I say u sredinu stola instead of u sredini stola? What’s the difference?

Yes, u sredinu stola is grammatically possible, but the meaning changes:

u sredini stola – locative → static location:
in the middle of the table (it is already there, not moving)
u sredinu stola – accusative → movement towards:
into the middle of the table (something is moving there)

In your sentence, the bowl is just located there, so u sredini stola (locative) is the correct choice.

Could I also say na sredini stola instead of u sredini stola?

Yes, na sredini stola is also natural and very common:

u sredini stola – literally in the middle (inside the area) of the table
na sredini stola – literally on the middle of the table

In practice, for a flat surface like a table, na sredini stola is probably even more common. Both are acceptable; the difference is very small in everyday speech.

Why is it stola and not stol in sredini stola?

Stola is the genitive singular of stol (table).

The pattern for many masculine nouns ending in a consonant:

nominative: stol (dictionary form)
genitive: stola

Here, sredina stola means the middle of the table, so genitive is required to express of the table.

Why is the verb stoji used here? Could we also use je?

Stoji literally means stands, is standing.

In Croatian you often describe the position of objects with verbs like:

stajati / stoji – to stand (upright object, or just neutrally placed)
ležati / leži – to lie
visjeti / visi – to hang

So U sredini stola stoji velika zdjela = In the middle of the table a big bowl is standing / stands.

You could say:

U sredini stola je velika zdjela.

This is also correct. Je (is) is more neutral and just states existence/location, while stoji adds a slight nuance of standing / placed there.

Why is the word order U sredini stola stoji velika zdjela and not Velika zdjela stoji u sredini stola?

Both versions are grammatically correct:

U sredini stola stoji velika zdjela.
– Emphasis starts with the location: In the middle of the table there is a big bowl…
Velika zdjela stoji u sredini stola.
– Starts by introducing the bowl: A big bowl stands in the middle of the table.

Croatian word order is flexible. You usually place at the beginning what you want to highlight or what is already known from context. Here, the speaker first paints the scene (in the middle of the table), then tells us what is there (a big bowl).

What exactly does the conjunction a mean here, and how is it different from i?

In the sentence:

..., a oko ruba stola su tanjuri.

A connects two clauses, but it often suggests:

contrast, opposition, or
a shift to another, somewhat different part of the scene.

Roughly:

i = and (simple addition)
a = and / while / whereas (mild contrast or shift)

So the idea is:

In the middle of the table there is a big bowl, *while around the edge of the table there are plates.*

Why do we say oko ruba stola? What cases are used there?

Oko as a preposition meaning around takes the genitive case.

In oko ruba stola:

ruba – genitive singular of rub (edge).
stola – genitive singular of stol (table).

So literally:

oko ruba stola = around the edge of the table
(around edge-of table – genitive + genitive)

Doesn’t oko mean “eye”? How can it mean “around” here?

Croatian has two separate words spelled oko:

oko (noun, neuter) – eye
- e.g. jedno oko, dva oka – one eye, two eyes
oko (preposition) – around, about
- e.g. oko kuće – around the house

They look the same in writing but are different words with different grammar and meaning. In oko ruba stola, it is the preposition around.

Why is it su tanjuri and not tanjuri su after oko ruba stola?

Su is the 3rd person plural of biti (to be), but it is also a clitic (an unstressed short word) in Croatian. Clitics tend to appear in second position in the clause.

In the clause oko ruba stola su tanjuri:

First element: oko ruba stola (a prepositional phrase)
Second position: su (the clitic verb)
Then: tanjuri (the subject)

You can say:

Oko ruba stola su tanjuri. ✓
But you normally wouldn’t say:
Oko ruba stola tanjuri su. ✗ (sounds wrong because su is not in the usual clitic position)

Can I omit su and just say ... a oko ruba stola tanjuri?

No, you cannot omit su here. Croatian does not normally drop the verb biti (to be) in the present tense the way some Slavic languages do.

You need su to form the present tense:

(Oni) su tanjuri. – They are plates.
Oko ruba stola su tanjuri. – Around the edge of the table there are plates.

Without su, the sentence would be ungrammatical or at least sound very incomplete.

Why is it tanjuri and not tanjure?

Tanjuri is nominative plural, while tanjure is accusative plural of tanjur (plate).

nominative plural: tanjuri – used for the subject of the sentence
accusative plural: tanjure – used for the direct object

In oko ruba stola su tanjuri, plates are the subject (the things that are around the edge), so nominative plural tanjuri is required. If they were the direct object, you might see tanjure instead.