Compre o bilhete online antes que nós cheguemos à estação.

Compre is the affirmative imperative form used with você in standard Brazilian Portuguese.

So this sentence is giving a command or instruction to you:

• você compra = you buy
• compre! = buy!

For você, Portuguese normally uses the present subjunctive form to make affirmative commands, which is why you get compre.

If the sentence were using tu, the command would usually be compra in standard grammar.

It can, but not necessarily.

Because compre is the command form for você, it may sound:

• neutral in many parts of Brazil, where você is the everyday word for you
• more polite than a very direct English command, depending on tone
• formal if the situation itself is formal

So Compre o bilhete online can simply sound like a normal instruction, not especially stiff.

Antes que is used when it is followed by a conjugated verb, as in:

• antes que nós cheguemos

In English, this is like before we arrive.

Portuguese has two common patterns here:

• antes que + subjunctive
• antes de + infinitive

So:

• antes que nós cheguemos à estação = before we arrive at the station
• antes de chegarmos à estação = before we arrive at the station

Both are possible, but the grammar after them is different.

Because after antes que, Portuguese normally uses the subjunctive.

Cheguemos is the present subjunctive form of chegar for nós.

This happens because the arrival has not happened yet. It is a future or uncertain event from the speaker’s point of view.

So:

• antes que nós cheguemos = before we arrive

Even though English uses a normal present form (arrive), Portuguese uses the subjunctive here.

No. Portuguese often leaves subject pronouns out because the verb ending already shows the subject.

So both are correct:

• antes que nós cheguemos à estação
• antes que cheguemos à estação

The version with nós can add:

• emphasis
• clarity
• a slightly more explicit rhythm

But grammatically, it is optional.

Because à is a contraction of:

• the preposition a
• the feminine article a

The verb chegar normally uses the preposition a in more formal or traditional grammar:

• chegar a algum lugar

And estação is a feminine noun that can take the article a:

• a estação

So:

• a + a estação → à estação

This accent is called crase.

A helpful comparison:

• chegar ao hotel = arrive at the hotel
• chegar à estação = arrive at the station

Yes — and that is very natural.

So you have two correct options:

• antes que nós cheguemos à estação
• antes de chegarmos à estação

The second version uses the personal infinitive: chegarmos.

This version is often a little more compact and very common in Portuguese.

Because the subject is we, you need chegarmos, not just chegar.

So:

• antes de chegarmos = before we arrive
• antes de chegar would usually mean before arriving, with a different or less specific subject

Because in Portuguese, online usually works naturally after the verb phrase or after the object.

So these are all possible:

• Compre o bilhete online
• Compre online o bilhete — possible, but less natural here
• Compre o bilhete pela internet — also natural

The version in your sentence sounds normal and idiomatic.

It depends on the type of ticket.

Bilhete is a real and correct word, and it can be used for things like:

• transit tickets
• entry tickets
• numbered tickets

But in Brazil, passagem is often more common for travel tickets, especially for:

• bus
• plane
• long-distance travel

So depending on context, a Brazilian might also say:

• Compre a passagem online antes que nós cheguemos à estação.

Both are possible, but passagem may sound more natural in some travel contexts.

In everyday spoken Brazilian Portuguese, a gente is very common.

So a more conversational version might be:

• Compre o bilhete online antes que a gente chegue à estação.

Notice the verb changes:

• nós cheguemos
• a gente chegue

Both mean we arrive, but:

• nós is a bit more standard or explicit
• a gente is very common in speech

So the original sentence is correct, but in casual conversation many Brazilians would likely prefer a gente.

Yes, it is grammatical and understandable.

That said, depending on context, a Brazilian might make it sound a bit more everyday by changing one or two parts, for example:

• Compre a passagem online antes que a gente chegue à estação.
• Compre o bilhete online antes de chegarmos à estação.

So the original sentence is good Portuguese, but there are slightly more colloquial alternatives that you may hear more often in Brazil.