Se você perder o metrô, espere por mim na estação principal.

In this sentence, perder is functioning as the future subjunctive, not the infinitive, even though for many verbs it looks identical to the infinitive.

After se when you are talking about a possible future situation, Portuguese often uses this pattern:

se + future subjunctive

So:

• Se você perder o metrô... = If you miss the subway...

This is very common in Portuguese for real future possibilities.

Compare:

• Se você perde o metrô... sounds more like a general or habitual situation in some contexts, and is not the normal choice here.
• Se você perder o metrô... is the standard way to say if you miss the subway in the future.

Espere is the imperative form used with você.

In Brazilian Portuguese, commands with você use the same form as the present subjunctive:

• esperar → espere

So:

• Espere por mim = Wait for me

This matches você, because você takes third-person singular verb forms.

Compare:

• você espera = you wait / you are waiting
• espere! = wait! said to você
• espera! is typically the tu command in varieties that use tu

So in this sentence, espere is correct because the speaker is addressing someone as você.

Even though você means you, it takes third-person singular verbs in Portuguese.

So you get:

• você perde
• você vai
• você espera
• se você perder
• espere

This is just how Portuguese grammar works. Historically, você comes from an older respectful expression, and it ended up behaving grammatically like a third-person form.

For English speakers, one of the main things to remember is:

• meaning = you
• grammar = third person singular

Espere mim is not correct.

With esperar, Portuguese can use either:

• esperar alguém
• esperar por alguém

In Brazil, esperar por is very common and natural, especially in everyday speech.

So:

• Espere por mim = Wait for me
• Me espere = also possible, and very common

Here, por mim means for me in the sense of wait for me.

So the sentence could also be phrased as:

• Se você perder o metrô, me espere na estação principal.

That would also sound natural in Brazilian Portuguese.

Na is a contraction of:

• em
  • a = na

So:

• na estação = in the station / at the station

Portuguese very often contracts prepositions with articles:

• em + o = no
• em + a = na
• de + o = do
• de + a = da

Since estação is feminine, it uses a, so:

• na estação principal

Because nouns in Portuguese have grammatical gender.

• metrô is masculine → o metrô
• estação is feminine → a estação

This affects the articles and other words that go with the noun.

So in the sentence:

• o metrô
• na estação principal = em + a estação principal

Unfortunately, noun gender often just has to be learned word by word, although some endings give useful clues. For example, nouns ending in -ção are usually feminine, so estação is feminine.

In Portuguese, adjectives often come after the noun.

So:

• estação principal = main station

This word order is very normal in Portuguese.

Some adjectives can go before the noun, but that may sound more formal, literary, or slightly different in emphasis. For a learner, the safest pattern is usually:

• noun + adjective

So estação principal is the expected and natural order.

Yes, the comma is normal here.

The sentence begins with a conditional clause:

• Se você perder o metrô

Then comes the main clause:

• espere por mim na estação principal

When this kind of introductory clause comes first, Portuguese normally uses a comma before the main clause.

So this punctuation is standard and helps the sentence read clearly.

Yes. Perder can mean both to lose and to miss, depending on context.

So:

• perder a chave = to lose the key
• perder o ônibus = to miss the bus
• perder o metrô = to miss the subway

This is very common in Portuguese. English uses different verbs, but Portuguese often uses perder for both ideas.

Yes, absolutely. That is a very natural alternative.

Both are correct:

• espere por mim na estação principal
• me espere na estação principal

The version with me espere is especially common in everyday Brazilian Portuguese.

The original sentence is also perfectly fine; it just uses esperar por alguém instead of placing the object pronoun before the verb.

It combines two different ideas:

1. Conditional future situation

   • Se você perder o metrô
   • This uses the future subjunctive

2. Command / instruction

   • espere por mim na estação principal
   • This uses the imperative for você

So the structure is:

• If X happens, do Y

This is a very useful everyday pattern in Portuguese:

• Se você chegar cedo, me ligue.
• Se chover, fique em casa.
• Se ele telefonar, avise-me.

Your sentence follows that same pattern.