Prije nego što krenemo na autocestu, svratit ćemo do benzinske postaje po vodu i gorivo.

It means before.

More literally, it is built from:

• prije = before
• nego što = than / before that

In this sentence, prije nego što krenemo na autocestu means before we head onto the highway.

In everyday English, you would usually translate the whole expression simply as before.

Yes. Prije nego što is a very common full form meaning before when it introduces a clause.

You may also hear:

• prije nego krenemo
• sometimes just prije nego što

For learners, prije nego što + verb is a safe and standard pattern to use.

So:

• Prije nego što krenemo... = Before we head off...

Because Croatian often uses the present tense after conjunctions like before, when, if, and similar time-related structures, even when the meaning is future.

So:

• Prije nego što krenemo... literally looks like Before we set off...
• but in English it naturally means Before we head off... / Before we leave...

This is normal in Croatian. The future meaning comes from the context, not from a future-tense form here.

It comes from the verb krenuti, which usually means:

• to set off
• to start going
• to head out

In this sentence, krenemo na autocestu means something like:

• we head onto the highway
• we set off onto the highway
• we start driving on the highway

It suggests the beginning of movement.

Because na can take different cases depending on meaning.

Here it expresses movement toward a destination, so it takes the accusative:

• na autocestu = onto the highway

Compare:

• Idemo na autocestu. = We are going onto the highway. → movement → accusative
• Mi smo na autocesti. = We are on the highway. → location → locative

So:

• na autocestu = onto the highway
• na autocesti = on the highway

It comes from svratiti, which means:

• to drop by
• to stop off
• to swing by

In this sentence, svratit ćemo do benzinske postaje means:

• we’ll stop by the gas station
• we’ll make a quick stop at the gas station

It usually suggests a short, purposeful stop, not a long visit.

In standard Croatian future tense, when ću / ćeš / će / ćemo / ćete / će comes after an infinitive ending in -ti, the -i drops in writing.

So:

• svratiti + ćemo → svratit ćemo

This is the standard written form.

You will sometimes see or hear svratiti ćemo, but standard Croatian prefers:

• svratit ću
• svratit ćeš
• svratit ćemo

Because the sentence begins with a subordinate clause:

• Prije nego što krenemo na autocestu = before we head onto the highway

Then comes the main clause:

• svratit ćemo do benzinske postaje po vodu i gorivo = we’ll stop by the gas station for water and fuel

Croatian normally separates this kind of introductory clause with a comma.

Do benzinske postaje literally means to the gas station in the sense of up to / as far as the gas station.

The preposition do takes the genitive:

• benzinska postaja → nominative
• do benzinske postaje → genitive

With svratiti, Croatian very often uses do + genitive to mean stop by / go over to a place:

• svratiti do trgovine = stop by the store
• svratiti do prijatelja = stop by a friend’s place

U benzinsku postaju would mean into the gas station, focusing more on entering the building.
But do benzinske postaje is the natural choice here for stop by the gas station.

Because after do, Croatian uses the genitive case.

The basic form is:

• benzinska postaja = gas station

After do, it changes to:

• do benzinske postaje

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

• benzinska → benzinske
• postaja → postaje

Here po means for, in the sense of to get / to fetch / to pick up.

So:

• svratiti po vodu i gorivo = stop by to get water and fuel

This is a very common Croatian pattern:

• ići po kruh = go get bread
• skoknuti po kavu = pop out for coffee
• svratiti po djecu = stop by to pick up the children

So this po is not the same as English on or by. It has the specific idea of going somewhere in order to obtain something.

Because po in this meaning takes the accusative case.

So:

• voda → vodu
• gorivo → gorivo

Why does only one of them visibly change?

• voda is a feminine noun, so its accusative singular is vodu
• gorivo is a neuter noun, and for neuter singular the accusative is the same as the nominative, so it stays gorivo

So:

• po vodu = for water
• po gorivo = for fuel

Because with verbs of movement, Croatian often uses po + accusative to mean go and get something.

So:

• Idem po kruh. = I’m going to get bread.
• Svratit ćemo po vodu i gorivo. = We’ll stop to get water and fuel.

If you used za, the meaning would be different and generally would not sound natural here.
For this idea of fetching / buying / picking up, po is the normal choice.

Not exactly. Gorivo means fuel in a general sense.

Depending on context, in English it could be:

• fuel
• gas
• petrol

Since the sentence mentions a gas station, an English translation might naturally say:

• water and gas
• water and fuel
• in British English, water and petrol

So gorivo is broader than just one specific fuel type.

Yes, Croatian word order is flexible.

This sentence starts with the time clause:

• Prije nego što krenemo na autocestu...

That puts the timing first and sounds very natural:

• Before we head onto the highway, we’ll stop by the gas station...

You could also rearrange it, for example:

• Svratit ćemo do benzinske postaje po vodu i gorivo prije nego što krenemo na autocestu.

That is also correct.
The original version simply sounds a bit more natural and organized because it sets up the timeline first.

Yes, both are typically perfective:

• krenuti = to set off, start moving
• svratiti = to drop by once, make a stop

That matters because the sentence describes single completed actions:

1. first, we make a stop
2. then, we set off onto the highway

Perfective verbs are very common when Croatian talks about one-time future actions like this.

Not very naturally.

A very literal version would be something like:

• Before than what we head onto the highway, we will drop by to the gas station for water and fuel.

That is not good English, but it shows the structure.

A natural English translation would be:

• Before we get on the highway, we’ll stop by the gas station for water and fuel.
• Before we head onto the highway, we’ll stop at the gas station for water and fuel.

So it is better to understand the Croatian structure rather than translate each word mechanically.