Αν δεν βρω βενζινάδικο ανοιχτό το βράδυ, θα βάλω βενζίνη αύριο το πρωί.

Because after αν in this kind of if-clause, Greek does not use θα.

Here, βρω is the aorist subjunctive form of βρίσκω (to find), and αν + subjunctive is the normal way to say if I find / if I don’t find when talking about a possible future situation.

So:

• Αν δεν βρω... = If I don’t find...
• not Αν δεν θα βρω...

A useful pattern to remember is:

• Αν + subjunctive, θα + future/result

In this sentence:

• Αν δεν βρω βενζινάδικο ανοιχτό το βράδυ = If I don’t find a gas station open at night / tonight
• θα βάλω βενζίνη αύριο το πρωί = I’ll get gas tomorrow morning

βρω is the aorist subjunctive of βρίσκω (to find).

Learners often expect something closer to the present stem, but Greek commonly uses the aorist subjunctive after αν when referring to a single completed action in the future.

So:

• βρίσκω = I find / I am finding
• να βρω = to find / that I find
• αν βρω = if I find

Why aorist here? Because the idea is finding something as a single event, not an ongoing process.

δεν is the normal negation used before verbs in many finite clauses, including this one.

So:

• βρω = I find
• δεν βρω = I don’t find

In this sentence:

• Αν δεν βρω... = If I don’t find...

Greek places δεν directly before the verb (or before the verb phrase), much like English don’t before find.

βενζινάδικο means gas station / petrol station.

It is a very common everyday word in Modern Greek and is not strange or slangy, though it feels more conversational than a more formal expression like:

• πρατήριο βενζίνης = petrol station / fuel station

So in normal speech, βενζινάδικο is exactly what many people would say.

Also notice that it is neuter:

• το βενζινάδικο = the gas station
• βενζινάδικο here is in the accusative singular, but for many neuter nouns the nominative and accusative look the same.

ανοιχτό means open, and here it describes βενζινάδικο.

So:

• βενζινάδικο ανοιχτό = an open gas station

This is a very common Greek structure: noun + adjective, often without an article when talking about some instance of a thing.

Also, ανοιχτό matches βενζινάδικο in gender, number, and case:

• βενζινάδικο = neuter singular
• ανοιχτό = neuter singular

So the agreement is correct.

It certainly could.

• Αν δεν βρω βενζινάδικο ανοιχτό...
• Αν δεν βρω ένα βενζινάδικο ανοιχτό...

Both are possible, but the version without ένα is very natural in Greek and often sounds a bit more general: if I don’t find any gas station open.

This is similar to how English sometimes says:

• If I don’t find a gas station open...

without putting heavy emphasis on the exact station.

So omitting ένα does not make the sentence incomplete.

Literally, το βράδυ means the evening / at night / in the evening, depending on context.

In this sentence, it most naturally refers to tonight / during the night this evening, because the speaker is making a plan:

• If I don’t find a gas station open tonight, I’ll get gas tomorrow morning.

Greek often uses time expressions with the definite article:

• το πρωί = in the morning
• το βράδυ = in the evening / at night
• το μεσημέρι = at noon / midday

So the article is completely normal here.

Yes, βάζω basically means put, and θα βάλω is its future form (I will put), but in Greek βάζω βενζίνη is the normal idiomatic way to say:

• get gas
• fill up with petrol
• put fuel in the car

So even though the literal meaning is something like I will put gasoline, the natural English translation is usually:

• I’ll get gas
• I’ll fill up tomorrow morning

This is one of those cases where translating word-for-word sounds odd in English, but it is perfectly natural in Greek.

βάλω is the aorist subjunctive / future base form of βάζω.

After θα, Greek uses this form to make the future:

• θα βάλω = I will put / I will get
• θα βάλω βενζίνη = I’ll get gas

This is very common in Modern Greek: the future is built with θα plus a verb form that often looks like the aorist subjunctive form.

Compare:

• βάζω = I put / I am putting
• θα βάλω = I will put

They refer to two different possible times:

• το βράδυ = the time when the speaker is trying to find a gas station open
• αύριο το πρωί = the later time when the speaker will get gas if that fails

So the logic of the sentence is:

1. Tonight / at night, I may try to find an open gas station.
2. If I don’t, then tomorrow morning I’ll get gas.

And again, notice the article in το πρωί. Greek commonly says:

• αύριο το πρωί = tomorrow morning
• αύριο το βράδυ = tomorrow evening

Yes, Greek word order is fairly flexible, though some orders sound more neutral than others.

The given sentence is perfectly natural:

• Αν δεν βρω βενζινάδικο ανοιχτό το βράδυ, θα βάλω βενζίνη αύριο το πρωί.

But you could also hear variations depending on emphasis, for example:

• Αν το βράδυ δεν βρω βενζινάδικο ανοιχτό, θα βάλω βενζίνη αύριο το πρωί.
• Αν δεν βρω το βράδυ βενζινάδικο ανοιχτό, θα βάλω βενζίνη αύριο το πρωί.

The original version is a nice neutral order.

Yes, absolutely.

Even though the Greek literally says If I don’t find, English often prefers can’t find in this context, because it sounds more natural when talking about availability.

So these are all reasonable translations:

• If I don’t find a gas station open tonight, I’ll get gas tomorrow morning.
• If I can’t find a gas station open tonight, I’ll get gas tomorrow morning.
• If I don’t find an open gas station tonight, I’ll get gas tomorrow morning.

They all match the Greek well.

The sentence follows a very common Greek conditional pattern:

• Αν + subjunctive for the condition
• θα + verb for the result

So:

• Αν δεν βρω βενζινάδικο ανοιχτό το βράδυ = condition
• θα βάλω βενζίνη αύριο το πρωί = result

You can use this pattern in many other sentences:

• Αν βρω χρόνο, θα έρθω. = If I find time, I’ll come.
• Αν δεν προλάβω, θα σε πάρω αύριο. = If I don’t make it in time, I’ll call you tomorrow.

It is one of the most useful everyday structures in Greek.