Se arrivi alle dodici e quindici, trovi ancora posto vicino alla finestra.

This is very normal in Italian.

In a real, likely condition, Italian often uses the present indicative in both parts:

• Se arrivi..., trovi...

Even if the meaning in English is future, Italian does not usually say the equivalent of if you will arrive, you will find.

So this sentence means something like:

• If you arrive at 12:15, you’ll still find a seat by the window.

This is one of the most common patterns in Italian:

• Se studi, passi l’esame.
• Se vieni presto, trovi posto.

Italian uses the present tense here where English often uses present + will.

Italian often leaves out subject pronouns because the verb ending already shows who the subject is.

• arrivi = you arrive
• trovi = you find

So tu is understood and does not need to be said.

You could say:

• Se tu arrivi alle dodici e quindici, trovi ancora posto...

but it sounds more marked, and you would usually only include tu for emphasis or contrast.

Se means if.

It introduces a condition:

• Se arrivi alle dodici e quindici... = If you arrive at 12:15...

This is one of the most basic uses of se in Italian.

Be careful not to confuse it with sé with an accent, which is a different word meaning himself/herself/itself in some contexts.

When telling time in Italian, you usually use a + article before the hour.

• all’una = at one
• alle due = at two
• alle dodici = at twelve

Here:

• a + le = alle

So:

• alle dodici e quindici = at 12:15

This is the standard way to say a specific time.

Yes. A very common alternative is:

• alle dodici e un quarto

Both mean at 12:15.

So you could also say:

• Se arrivi alle dodici e un quarto, trovi ancora posto vicino alla finestra.

Both are correct.
dodici e quindici is more directly numerical, while dodici e un quarto is more like a quarter past twelve.

Here ancora means still.

So:

• trovi ancora posto = you still find a seat / there is still a seat available

It suggests that seats may soon be gone, but at that time there is still availability.

Depending on context, ancora can also mean again, so it is a useful word whose meaning depends on the sentence.

In Italian, trovare posto is a very common expression meaning:

• to find space
• to find a seat
• to find room

So posto is often used without an article in this kind of general sense.

Compare:

• trovare posto = find space / find a seat
• trovare un posto = find a place / a seat
• trovare il posto = find the place / the seat

In your sentence, trovi ancora posto sounds natural and idiomatic: it means there is still room available, especially in a restaurant, train, waiting room, etc.

Vicino a means near or close to.

So:

• vicino alla finestra = near the window / by the window

The form alla is just:

• a + la = alla

Because finestra is a feminine singular noun, its article is la:

• la finestra = the window
• a la finestra becomes alla finestra

So:

• vicino alla finestra = near the window

Literally, posto means place, but in this sentence it most naturally means seat or spot available.

So depending on context, the sentence could suggest:

• a seat in a restaurant
• a place on a train
• a spot in a room

Italian often uses posto where English might choose seat, space, or spot.

It is normal to use a comma here because the sentence starts with the se-clause:

• Se arrivi alle dodici e quindici, trovi ancora posto...

This helps separate the condition from the result.

If you reverse the order, the comma is often omitted:

• Trovi ancora posto vicino alla finestra se arrivi alle dodici e quindici.

So the comma is not about a special grammar rule unique to Italian; it is mainly standard punctuation for clarity.

Yes. The verbs arrivi and trovi are in the second person singular, so the sentence is addressing you informally.

If you wanted the formal Lei form, you would say:

• Se arriva alle dodici e quindici, trova ancora posto vicino alla finestra.

That is the polite singular form.

So your original sentence is the natural choice when speaking to a friend, family member, classmate, or someone you address with tu.

Word-for-word, parts of it match, but that would sound unnatural in English.

A more natural English translation would be:

• If you arrive at 12:15, you can still get a seat by the window.
• If you arrive at 12:15, you’ll still find a seat by the window.

This is a good example of how Italian and English often use slightly different natural phrasing, even when the grammar is straightforward.

Yes. Italian allows some flexibility.

For example:

• Se arrivi alle dodici e quindici, trovi ancora posto vicino alla finestra.
• Trovi ancora posto vicino alla finestra se arrivi alle dodici e quindici.

Both are correct.

The version with Se... first emphasizes the condition first.
The version with Trovi... first emphasizes the result first.

The original order is very natural and common.