Na benzinskoj postaji ćemo kupiti vodu i sendvič.

For places like a gas station, Croatian normally uses na, not u.

So:

• na benzinskoj postaji = at the gas station
• u usually means in/inside, but with some locations Croatian simply prefers na by convention

This is something you often just have to learn with the noun or place expression. Compare:

• na pošti = at the post office
• na kolodvoru = at the station
• na benzinskoj postaji = at the gas station

So even if English says at or sometimes in, Croatian chooses the preposition that sounds natural with that place.

It is in the locative singular, because na is expressing a location here.

The base form is:

• benzinska postaja = gas station

After na meaning at/on/in a place, it becomes:

• na benzinskoj postaji

Both words change because adjectives and nouns must agree in:

• gender
• number
• case

So:

• benzinska → benzinskoj
• postaja → postaji

This agreement is very important in Croatian.

Both are direct objects of kupiti, so both are in the accusative.

But different noun types form the accusative differently.

1. voda → vodu

Voda is a feminine noun ending in -a, and in the accusative singular that usually changes to -u:

• voda → vodu
• knjiga → knjigu
• kava → kavu

2. sendvič → sendvič

Sendvič is a masculine inanimate noun. In Croatian, masculine inanimate nouns usually have:

• nominative = accusative

So:

• sendvič → sendvič

If it were a masculine animate noun, the accusative would usually change:

• pas → psa

Ćemo kupiti means we will buy.

It is made from:

• ćemo = we will
• kupiti = to buy

So the structure is:

• future auxiliary + infinitive

The verb ćemo comes from htjeti (to want), but in modern Croatian future tense it works like an auxiliary:

• ja ću kupiti = I will buy
• mi ćemo kupiti = we will buy

Because kupiti is perfective, and it fits the idea of a single completed action: we will buy.

Croatian often distinguishes between:

• kupiti = to buy, to complete the purchase
• kupovati = to be buying, to buy habitually, to do shopping

In this sentence, the meaning is a simple future result:

• we will buy water and a sandwich

So kupiti is the natural choice.

If you said kupovati, it would suggest a different nuance, such as repeated action or the process of shopping.

Because ćemo is a clitic. Clitics are short unstressed words that usually appear near the beginning of the clause, often after the first phrase.

So this word order is normal:

• Na benzinskoj postaji ćemo kupiti vodu i sendvič.

The first unit is Na benzinskoj postaji, and ćemo comes right after it.

Croatian word order is flexible, so you can also hear or see:

• Kupit ćemo vodu i sendvič na benzinskoj postaji.
• Vodu i sendvič ćemo kupiti na benzinskoj postaji.

These all mean basically the same thing, but the emphasis shifts a little.

Yes. That is very common and fully correct.

So these are both natural:

• ćemo kupiti
• kupit ćemo

When the future auxiliary comes directly after the infinitive, Croatian normally shortens the infinitive:

• kupiti + ćemo → kupit ćemo

This happens in standard writing:

• pisati ćemo → standard pisat ćemo
• kupiti ćemo → standard kupit ćemo

So if the infinitive comes first, the standard form is kupit ćemo, not kupiti ćemo.

Yes, both mean gas station / petrol station.

• benzinska postaja
• benzinska stanica

Both are understood. Depending on region, habit, or style, one may be more common than the other. A learner should recognize both.

So:

• Na benzinskoj postaji...
• Na benzinskoj stanici...

Both are normal Croatian.

Because Croatian does not have articles like English.

So Croatian simply says:

• vodu = water / the water / some water
• sendvič = a sandwich / the sandwich

The exact meaning depends on context.

English requires articles, but Croatian usually does not mark that distinction directly. Learners often need time to get used to that.

Yes. Croatian has much freer word order than English because case endings show the grammatical relationships.

These are all possible:

• Na benzinskoj postaji ćemo kupiti vodu i sendvič.
• Kupit ćemo vodu i sendvič na benzinskoj postaji.
• Vodu i sendvič ćemo kupiti na benzinskoj postaji.

The core meaning stays the same, but the focus changes:

• starting with Na benzinskoj postaji emphasizes the location
• starting with Kupit ćemo emphasizes the action
• starting with Vodu i sendvič emphasizes what will be bought

So Croatian word order is flexible, but it is not random: it often reflects emphasis and information structure.