Compramos la entrada anticipada antes de visitar el puesto de fanzines.

Here compramos means we bought, so it is the preterite.

A useful thing to know is that compramos can also mean we buy in the present tense. For -ar verbs, the nosotros form is often identical in the present and preterite:

• compramos = we buy
• compramos = we bought

So you understand it from context. Since the meaning has already been given as a past action, this sentence is using the preterite.

Yes. On its own, compramos is ambiguous.

For example:

• Todos los años compramos entradas anticipadas. = Every year we buy advance tickets.
  Here it is present/habitual.

• Ayer compramos la entrada anticipada. = Yesterday we bought the advance ticket.
  Here it is clearly past.

Spanish often relies on context, time expressions, or the wider conversation to make the meaning clear.

La entrada means the ticket or the admission ticket, so it sounds like a specific ticket that both speaker and listener can identify from context.

Spanish uses the definite article quite often where English may or may not use the. If you said una entrada anticipada, it would mean an advance ticket, with a more indefinite or first-mention feel.

So the difference is roughly:

• la entrada anticipada = the advance ticket
• una entrada anticipada = an advance ticket

In Spain, entrada is the normal word for an admission ticket to an event, venue, exhibition, concert, etc.

Compare:

• entrada = ticket for entry/admission
• billete = ticket for transport, like a train or bus ticket
• boleto = common in much of Latin America, but less standard in Spain for this meaning

So in Spain, compramos la entrada anticipada sounds natural for buying entry to something.

In Spanish, descriptive adjectives usually come after the noun.

So:

• entrada anticipada = advance ticket

This is the normal word order. Also, the adjective must agree with the noun:

• entrada is feminine singular
• so the adjective is anticipada, also feminine singular

That is why it is:

• la entrada anticipada not
• la entrada anticipado

Literally, anticipada means something like advanced or in advance. In this context, entrada anticipada means a ticket bought ahead of time, usually before the day of the event or before arriving at the place.

In natural English, you would often translate it as:

• advance ticket
• ticket bought in advance

So anticipada is describing the ticket as being obtained earlier than usual.

Because antes is followed by de before an infinitive.

The pattern is:

• antes de + infinitive

So:

• antes de visitar = before visiting

This is a very common structure in Spanish:

• antes de salir = before leaving
• antes de comer = before eating
• antes de entrar = before entering

Without de, it would be ungrammatical here.

After antes de, Spanish uses the infinitive when the subject of both actions is the same.

In this sentence, the implied subject is we for both verbs:

• Compramos... = We bought...
• antes de visitar... = before visiting... / before we visited...

Since the same people do both actions, Spanish uses antes de + infinitive.

If the subject changes, Spanish normally uses:

• antes de que + subjunctive

For example:

• Compramos la entrada antes de que abriera el puesto.
  = We bought the ticket before the stall opened.

Because visitar normally takes a direct object with no preposition.

So you say:

• visitar el museo
• visitar la tienda
• visitar el puesto

The personal a is used mainly with specific people (and sometimes pets), not with places or stalls.

So:

• visitar a María = to visit María
• visitar el puesto = to visit the stall

Puesto here means a stall, stand, or booth, especially at a market, fair, convention, or event.

So el puesto de fanzines means:

• the fanzine stall
• the fanzine booth
• the stand selling fanzines

The structure noun + de + noun is very common in Spanish to show what something is for, contains, or sells:

• tienda de ropa = clothes shop
• puesto de comida = food stall
• puesto de fanzines = fanzine stall

Yes. Fanzine is used in Spanish too, as a borrowed word.

Its plural is formed normally:

• fanzine = one fanzine
• fanzines = more than one

So puesto de fanzines simply means the stall had more than one fanzine, or that it was a stall for fanzines in general.

In Spain, many speakers pronounce the z with the Castilian th sound, roughly like fan-thi-nes.

Yes. A very natural alternative is:

• Antes de visitar el puesto de fanzines, compramos la entrada anticipada.

This means the same thing: Before visiting the fanzine stall, we bought the advance ticket.

Spanish word order is flexible enough to move the time phrase to the beginning for emphasis or style. The original version is also completely natural.