أنتظر خارج المحطة.

In Arabic, the verb itself usually shows the subject.

• أنتظر is the 1st person singular form of the imperfect verb.
• The prefix أَ- on the verb tells you the subject is I.

So Arabic often does not need أنا here.

• أنتظر خارج المحطة = I wait / I am waiting outside the station
• أنا أنتظر خارج المحطة = also possible, but أنا adds emphasis, like I am waiting outside the station.

أنتظر is in the imperfect tense. In Modern Standard Arabic, the imperfect can cover several meanings that English separates:

• I wait
• I am waiting
• sometimes even I will wait, depending on context

In this sentence, the natural meaning is usually I am waiting or I wait.

If you want to make the future clearer, Arabic often adds a future marker such as:

• سأنتظر = I will wait
• سوف أنتظر = I will wait

The dictionary form is اِنْتَظَرَ = to wait.

The form in the sentence, أنتظر, is the imperfect 1st person singular of that verb.

A basic pattern is:

• اِنْتَظَرَ = he waited
• يَنْتَظِرُ = he waits / is waiting
• أَنْتَظِرُ = I wait / am waiting

This verb is commonly taught as a Form VIII verb.

Arabic usually does not use a separate present-tense verb to be like English am / is / are.

So where English says:

• I am waiting

Arabic just says:

• أنتظر

The present meaning is understood from the verb form itself.

خارج means outside.

In sentences like this, it often behaves like an adverb of place or a preposition-like word:

• خارج المحطة = outside the station

So it tells you where the waiting happens.

You can think of it as functioning very much like outside in English.

خارج can stand alone if the place is already understood, but here it is followed by the place being referred to:

• خارج المحطة = outside the station

The noun after خارج specifies outside of what.

Grammatically, المحطة is connected to خارج in an iḍāfa-like relationship, so المحطة is in the genitive sense.

In fully vocalized Arabic, you would see this as:

• خارجَ المحطّةِ

But in normal writing, those case endings are usually not written.

الـ is the Arabic definite article, meaning the.

So:

• محطة = a station / station
• المحطة = the station

In your sentence, it is a specific station, so المحطة is used.

المحطة comes from a root connected with the idea of stopping or halting.

So محطة is literally a stop/station.

Depending on context, it can mean:

• station
• stop
• terminal

In this sentence, station is the natural meaning.

A careful pronunciation is roughly:

• ʾantaẓiru khārija al-maḥaṭṭah

More precisely in full case-marked form:

• أَنْتَظِرُ خارِجَ المَحَطَّةِ

A few pronunciation notes:

• ظ in أنتظر is an emphatic z-like sound
• خ in خارج is like the ch in Scottish loch or German Bach
• ح in المحطة is a strong breathy h
• ط is an emphatic t
• the doubled طّ in المحطة is pronounced longer

That is normal in everyday Arabic writing.

Most Arabic texts are written without full short-vowel marks, so learners have to know the word forms from vocabulary and grammar.

So the unvocalized sentence is:

• أنتظر خارج المحطة

But a fully vocalized version would be:

• أَنْتَظِرُ خَارِجَ الْمَحَطَّةِ

This is one reason Arabic reading takes practice: the reader often supplies the missing vowels.

This is a very normal Arabic sentence pattern.

Arabic often uses:

• verb + complement
• verb + adverb/place expression

So:

• أنتظر خارج المحطة
  literally follows the pattern
• [I wait] [outside the station]

Since the subject I is already built into the verb, nothing else is required.

Yes. That is grammatical.

The difference is mainly emphasis:

• أنتظر خارج المحطة = neutral, natural
• أنا أنتظر خارج المحطة = I am waiting outside the station

Adding أنا can make the subject more explicit or contrastive.

It can do both, depending on the sentence.

By itself here:

• أنتظر خارج المحطة = I am waiting outside the station

If you want to say I am waiting for my friend, Arabic can say:

• أنتظر صديقي = I am waiting for my friend

So unlike English, Arabic often does not need a separate word like for after انتظر.

In fully inflected MSA, the sentence would typically be:

• أَنْتَظِرُ خارِجَ المَحَطَّةِ

Here is why:

• أنتظرُ: the verb is in the imperfect and normally ends in -u
• خارجَ: functioning as an adverbial expression of place, so it is in the accusative
• المحطةِ: genitive after خارج in this construction

In normal modern writing and speech, these case endings are often not shown or not fully pronounced, especially outside very formal reading styles.