Quan tenim temps, la meva mare i jo entrem a la llibreria per mirar llibres.

Because Quan tenim temps is an introductory time clause. In Catalan, when a subordinate clause comes before the main clause, a comma is normally used:

Quan tenim temps, ...

If the order were reversed, the comma would usually disappear:

La meva mare i jo entrem a la llibreria per mirar llibres quan tenim temps.

It can feel like both. Grammatically, quan means when, but in a sentence like this, with the present tense and a habitual meaning, English often uses whenever naturally.

So Quan tenim temps can mean:

• When we have time
• or more naturally in context, Whenever we have time

Because Catalan often uses the present tense for habits and repeated actions, just like English does in sentences such as When we have time, we go into the bookstore.

So here:

• tenim = we have
• entrem = we go in / we enter

This does not have to mean only right now. It can describe something that happens regularly.

Catalan is a pro-drop language, which means subject pronouns are often omitted because the verb form already shows who the subject is.

So:

• tenim already means we have
• entrem already means we enter / go in

You could add nosaltres for emphasis, but it is not necessary:

• Quan nosaltres tenim temps...
  This sounds more emphatic than neutral.

In Catalan, possessives are very often used together with the definite article.

So the normal pattern is:

• la meva mare = my mother
• el meu pare = my father
• els meus amics = my friends

For an English speaker, this feels unusual because English normally says just my mother, without the. But in Catalan, la meva mare is the standard form.

Both are possible grammatically. The order is flexible.

However, putting yourself second often sounds more natural or polite, much like in English:

• my mother and I

So la meva mare i jo is a very natural choice.

Entrem comes from entrar, meaning to enter or to go in.

In this sentence, it suggests actually going inside the bookstore, not just going toward it.

So the difference is roughly:

• anem a la llibreria = we go to the bookstore
• entrem a la llibreria = we go into the bookstore / we enter the bookstore

Yes. Llibreria means bookstore or bookshop, not library.

The Catalan word for library is biblioteca.

So:

• llibreria = bookstore
• biblioteca = library

This is a very common mistake for English speakers.

Because a is the preposition used here before the destination.

• a = to / into, depending on context
• la llibreria = the bookstore
• a + la stays a la

So entrem a la llibreria means we go into the bookstore / we enter the bookstore.

Per + infinitive is a very common way in Catalan to express purpose: to, in order to.

So:

• per mirar llibres = to look at books / in order to look at books

It explains why they go into the bookstore.

Also, mirar here means to look at, not necessarily to read. In context, it can suggest browsing.

Because llibres is being used in a general, non-specific sense.

• mirar llibres = look at books / browse books in general
• mirar els llibres = look at the books, meaning specific books already known in the conversation

So the absence of the article makes the meaning more general.

It is not singular: entrem is the first-person plural form, meaning we enter / we go in.

In Catalan, when the subject includes jo plus someone else, the verb goes in the we form:

• la meva mare i jo entrem
• el meu amic i jo tenim

That is the same logic as English my mother and I go in, not my mother and I goes in.

In standard Catalan, ll is usually pronounced as a palatal l sound, written /ʎ/ in phonetics. For many English speakers, a rough approximation is the lli sound in million, though it is not exactly the same.

So:

• llibreria
• llibres

Both begin with that ll sound, not a normal English l. Depending on the dialect, pronunciation can vary somewhat, but for learners, recognizing ll as a special Catalan sound is the important first step.