En cuanto entramos, buscamos el puesto de fanzines.

En cuanto means as soon as or the moment that. It emphasizes that one action happens immediately after another.

• En cuanto entramos, buscamos... = As soon as we went in, we looked for...
• Cuando entramos, buscamos... = When we went in, we looked for...

Both can work, but en cuanto gives a stronger sense of immediacy.

They are both in the preterite because the sentence describes completed actions in the past.

• entramos = we entered / we went in
• buscamos = we looked for

The idea is:

1. we entered
2. right after that, we looked for the stall

In Spanish, the preterite is very common for a sequence of completed events like this.

By itself, entramos can be ambiguous, because it can also be the present tense form meaning we enter.

However, in this sentence, the context makes it clearly past:

• En cuanto entramos, buscamos...

Since buscamos is also naturally understood here as a past action, the whole sentence is read as a past narrative.

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

• entramos already tells you it is we
• buscamos already tells you it is we

So nosotros is unnecessary unless you want extra emphasis or contrast.

For example:

• En cuanto nosotros entramos... would sound more marked, as if you were contrasting we with someone else.

Here, puesto means a stall, stand, or booth.

In Spain, puesto is very commonly used for a place where things are sold, especially at:

• markets
• fairs
• festivals
• comic or zine events

So el puesto de fanzines is the stall or booth where fanzines are being sold or displayed.

Using el suggests a specific stall that the speakers had in mind.

• el puesto de fanzines = the fanzine stall
• un puesto de fanzines = a fanzine stall

So this sentence sounds like they already knew there was a particular stall they wanted to find.

De is used here to show what kind of stall it is.

• puesto de fanzines = stall of fanzines, more naturally fanzine stall

This is a very common Spanish pattern:

• tienda de ropa = clothes shop
• puesto de comida = food stall
• mesa de información = information desk

So de often corresponds to an English noun used like an adjective.

You could, but it would not mean quite the same thing.

• el puesto de fanzines = the stall whose purpose or identity is selling/displaying fanzines
• el puesto con fanzines = the stall with fanzines

Con just describes what is there. De is the normal choice for naming the type of stall.

The comma separates the introductory time clause from the main clause:

• En cuanto entramos, = introductory clause
• buscamos el puesto de fanzines. = main clause

This is also common in English:

• As soon as we went in, we looked for the fanzine stall.

The comma helps the sentence read more clearly.

Yes. Fanzine is used in Spanish too, especially in cultural, comic, indie, and DIY contexts. Its plural is fanzines.

So:

• un fanzine
• dos fanzines

It is a borrowed word, but it is well understood in the right contexts.

Yes, in many contexts you could say:

• Al entrar, buscamos el puesto de fanzines.

That means something like on entering or when we went in.

The difference is:

• en cuanto entramos stresses immediately after entering
• al entrar is a bit more neutral and can sound slightly more general or stylistic

Both are natural, but en cuanto is better if you want to stress as soon as.

Yes. In Spanish, buscar normally takes a direct object, with no preposition.

• buscamos el puesto
• busco mis llaves
• están buscando una farmacia

This is different from English, where we usually say look for.

So:

• English: look for the stall
• Spanish: buscar el puesto

That is completely normal.