Després del sopar, vam mirar les postres.

Because del is the normal contraction of de + el in Catalan.

• de = of / from / after in some contexts
• el = the
• de + el = del

So:

• després del sopar = after dinner
• literally, after the dinner

This is very similar to Spanish del. In Catalan, using de el here would sound wrong.

Because després normally works with de when it introduces what comes after.

So:

• després de classe = after class
• després del sopar = after dinner
• després de treballar = after working

You can think of després de as a fixed expression meaning after.

Vam mirar is the periphrastic past, one of the most common ways to talk about completed past actions in Catalan.

It is made with:

• a form of anar (to go) used as an auxiliary
• • the infinitive

Here:

• vam = first person plural auxiliary form
• mirar = to look at / to watch

So vam mirar means:

• we looked at
• sometimes, depending on context, we watched

In this sentence, it refers to a completed action in the past.

Because vam mirar and miràvem express different kinds of past.

• vam mirar = completed action in the past
• miràvem = ongoing, repeated, or background action in the past

So:

• Després del sopar, vam mirar les postres.
  = After dinner, we looked at the desserts.
  This sounds like a single completed event.

But:

• Després del sopar, miràvem les postres mentre parlàvem.
  = After dinner, we were looking at the desserts while we were talking.
  This suggests an ongoing scene.

Yes, les postres is very commonly used in the plural in Catalan, just as in Spanish.

So:

• les postres = dessert / desserts / pudding course, depending on context

Even when English often uses singular dessert, Catalan frequently uses the plural form. It can refer to:

• the dessert course in general
• the desserts available
• sweet things served after the meal

So in this sentence, les postres is perfectly natural.

Literally, mirar means to look at. In this sentence, it most naturally means something like:

• we looked at the desserts
• we checked out the desserts
• possibly we had a look at the dessert options

Depending on context, it can imply they were considering them, but mirar itself does not directly mean to choose. If you wanted to say we chose the desserts, Catalan would more likely use a verb like triar or escollir.

Because Després del sopar is an introductory time expression, and it is very natural to separate it from the main clause with a comma.

So the sentence has this structure:

• Després del sopar = time phrase
• vam mirar les postres = main clause

The comma helps readability. In some short sentences, punctuation can vary, but this comma is completely normal and standard.

Yes, you could also say:

• Vam mirar les postres després del sopar.

That means the same thing. The difference is mostly one of emphasis and flow.

• Després del sopar, vam mirar les postres.
  starts by setting the time frame
• Vam mirar les postres després del sopar.
  starts with the action

Both are natural Catalan.

In Catalan, definite articles are often used more than in English. Here, les postres sounds natural because it refers to the dessert course or the desserts in that situation.

So:

• vam mirar les postres = we looked at the desserts / the dessert menu / dessert options

Leaving out the article would usually sound less natural here. Catalan often prefers the article where English might be more flexible.

A simple approximate pronunciation for an English speaker is:

des-PRES del soo-PAR, bam mee-RAR ləz POS-trəs

A few helpful points:

• després has stress on the last syllable: després
• sopar also has final stress: sopar
• vam is pronounced with a b/v sound that in most Catalan varieties sounds like b
• mirar has stress on the last syllable: miRAR
• les is often pronounced with a weak vowel, roughly like ləz
• postres has two syllables, roughly POS-tres or POS-trəs, depending on accent

Pronunciation varies a bit by dialect, but this approximation is a good start.