Si vols l'entrada del concert, te la compro dilluns després de la feina.

In this sentence, si means if, and Catalan normally uses the indicative after si for a real or possible condition.

So:

• si vols = if you want
• vols is the 2nd person singular present of voler = to want

This is completely normal Catalan. A subjunctive is not used here.

Because the feminine singular article la becomes l' before a word beginning with a vowel or silent h.

So:

• la entrada ➝ l'entrada

This is the same kind of apostrophe you see in many Catalan articles and pronouns.

Yes. Entrada can mean both:

• entrance
• ticket / admission ticket

With events such as concerts, films, or matches, entrada very often means ticket.

So l'entrada del concert means the concert ticket.

Del is the contraction of:

• de + el = del

So:

• el concert = the concert
• l'entrada del concert = literally the ticket of the concert

In natural English, that usually becomes the concert ticket or the ticket for the concert.

These are weak pronouns (clitic pronouns).

• te = to you / for you
• la = it, referring back to l'entrada, which is feminine singular

So:

• te la compro = I’ll buy it for you

The pronoun la has to be feminine because entrada is feminine.

Because Catalan clitic pronouns follow a fixed order, and in this kind of combination the indirect object comes before the direct object.

Here:

• te = indirect object
• la = direct object

So the correct order is:

• te la

not:

• la te

This is just one of the standard pronoun-order patterns you have to learn.

When the 2nd person singular pronoun combines with another clitic, Catalan uses te in the cluster.

So you get:

• te la
• te'l
• te'n

But when the pronoun is by itself before the verb, you often see et:

• Et compro una entrada = I buy you a ticket / I’ll buy a ticket for you

So te la compro is the normal combined form.

Catalan often uses the present tense to talk about a future action, especially when there is a time expression that makes the future clear.

Here, dilluns already tells you when the action will happen, so:

• te la compro dilluns = I’ll buy it for you on Monday

This is very natural. You could also say:

• te la compraré dilluns

Both are correct. The future form is a bit more explicitly future, but the present is extremely common.

Catalan often uses the day of the week without a preposition.

So:

• dilluns = on Monday

This is very normal.

A few useful comparisons:

• dilluns = on Monday / Monday
• els dilluns = on Mondays / every Monday

So in this sentence, dilluns refers to a specific Monday, understood from context.

Because després normally takes the preposition de before a noun, pronoun, or infinitive.

So you get:

• després de la feina = after work
• després d'això = after that
• després de dinar = after eating / after lunch

So de is required here.

Catalan uses the definite article more often than English does.

So English says:

• after work

but Catalan naturally says:

• després de la feina

Here la feina means work, the job, or the workday, depending on context. In this sentence it simply means after work in the everyday sense.

Yes. That is also correct.

Compare:

• te la compro dilluns = present with future meaning; very natural in everyday speech
• te la compraré dilluns = explicit future; also completely correct

So the difference is mostly one of style and emphasis, not basic meaning.