Després de sopar, vull dormir aviat.

In Després de sopar, the word sopar is being used as an infinitive verb, meaning to have dinner / to eat dinner.

After després de (after), Catalan often uses an infinitive:

• després de menjar = after eating
• després de treballar = after working
• després de sopar = after having dinner

It is true that sopar can also be a noun in some contexts, but here the structure clearly works like after + verb.

Després de means after.

It is commonly followed by:

• a noun: després del sopar = after the dinner / after dinner
• an infinitive: després de sopar = after having dinner

In this sentence, després de sopar is the natural way to say after dinner / after having dinner.

Catalan often drops subject pronouns when they are not needed, because the verb ending already shows the subject.

• vull = I want
• vols = you want
• vol = he/she/it wants

So vull dormir aviat already clearly means I want to sleep early.
You could say jo vull dormir aviat for emphasis, but it is not necessary.

Because with voler (to want), Catalan normally uses directly + infinitive:

• vull dormir = I want to sleep
• vull menjar = I want to eat
• vull marxar = I want to leave

No extra preposition is needed.
This is similar to English want to sleep, except Catalan does not insert a separate word equivalent to English to before the second verb in this structure.

Here aviat means early / soon, depending on context.

In vull dormir aviat, it means early:

• I want to go to sleep early

But in other contexts, aviat can mean soon:

• Tornaré aviat = I’ll come back soon

So the exact English translation depends on the sentence.

Literally, dormir means to sleep.
But in sentences like this, English often prefers go to sleep or go to bed early.

So:

• vull dormir aviat literally = I want to sleep early
• more natural English meaning = I want to go to sleep early

Catalan uses dormir more broadly here than English often does.

Yes, the order can be different.

The sentence starts with a time expression:

• Després de sopar = after dinner

Then comes the main clause:

• vull dormir aviat = I want to sleep early

This order is very natural because it sets the scene first. But Catalan can also say:

• Vull dormir aviat després de sopar

That said, Després de sopar, vull dormir aviat sounds very natural and clear.

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

• Després de sopar, = after dinner,
• vull dormir aviat. = I want to sleep early.

This is similar to English punctuation.
The comma is helpful and natural here, especially in writing, although punctuation can sometimes vary depending on style.

The accent in després shows the stressed vowel and helps distinguish correct pronunciation.

It is pronounced with stress on the last syllable:

• des-prés

Catalan uses accent marks more regularly than English to show stress or vowel quality. So the accent is an important part of the correct spelling.

A simple pronunciation guide is:

des-PRES de so-PAR, vuy door-MEER uh-vee-AHT

A few notes:

• després has stress on the last syllable
• sopar also has stress on the last syllable
• vull sounds roughly like vuy in central Catalan
• dormir has stress on -mir
• aviat has stress on the last syllable

Pronunciation varies somewhat by dialect, but this will help a learner say it understandably.

Yes, but the meaning shifts slightly.

• després de sopar = after having dinner / after dinner in a general sense
• després del sopar = after the dinner / after that meal

So després de sopar is the more general and idiomatic version for everyday speech.
Després del sopar sounds more specific, as if referring to a particular dinner.

It is neutral and natural, so it works in both everyday speech and normal writing.

Nothing in the sentence is especially formal or especially casual:

• després de is standard
• vull is standard
• dormir aviat is a normal everyday expression

So it is a very useful model sentence for learners.