Avui el pis està desordenat, i he d'endreçar el pis abans de sopar.

Here pis means apartment or flat.

A useful note:

• In Catalan, pis often means a flat/apartment, especially in Spain.
• In other contexts, pis can also mean floor/storey of a building.

So in this sentence, el pis = the apartment / the flat.

Catalan often uses estar for a state or condition, especially one that can change.

So:

• està desordenat = is messy / is untidy as a current condition
• és desordenat would more likely describe something as messy by nature or generally untidy

In this sentence, the apartment is messy right now, so està is the natural choice.

He d'endreçar means I have to tidy up or I need to tidy up.

This is the structure:

• haver de + infinitive = to have to / to need to
• he de = I have to
• endreçar = to tidy up / to put in order

So:

• he d'endreçar el pis = I have to tidy up the apartment

Because de becomes d' before a word starting with a vowel.

So:

• he de endreçar → he d'endreçar

This is just a normal contraction in Catalan pronunciation and spelling.

You will see the same thing in many places:

• d'anar
• d'estudiar
• d'obrir

Catalan can repeat the noun instead of replacing it immediately with a pronoun, especially when the speaker wants to be clear.

So:

• Avui el pis està desordenat, i he d'endreçar el pis... is perfectly natural.

But Catalan could also use a pronoun:

• Avui el pis està desordenat, i l'he d'endreçar abans de sopar.

That means the same thing:

• I have to tidy it up before dinner

So the repetition is not wrong; it is just a full, clear way of saying it.

Endreçar means to tidy up, to put in order, or to straighten up.

It is often used for:

• a room
• a house
• a desk
• objects that are out of place

It is very close to:

• tidy up
• put things away
• organize

In this sentence, endreçar el pis means to tidy up the apartment.

Literally, it means before dining / before having dinner.

Structure:

• abans de = before
• sopar = to have dinner (infinitive here)

So Catalan uses:

• abans de + infinitive

Examples:

• abans de marxar = before leaving
• abans de dormir = before sleeping
• abans de sopar = before having dinner

In natural English, this is often translated simply as before dinner.

Here it is a verb.

Why? Because after abans de, Catalan commonly uses an infinitive:

• abans de sopar = before having dinner

But sopar can also relate to dinner more generally, depending on context.

Compare:

• Sopem a les vuit. = We have dinner at eight.
• El sopar és a les vuit. = Dinner is at eight.

So in your sentence, sopar is verbal, even though English may translate it more simply as before dinner.

Avui means today, and putting it at the beginning is very natural because it sets the time frame right away.

Catalan is fairly flexible with adverb placement, but sentence-initial position is common for time expressions:

• Avui el pis està desordenat...

This is similar to English:

• Today, the apartment is messy...

It gives the sentence a natural topic: today.

Because desordenat agrees with el pis, which is:

• masculine
• singular

So the adjective is also masculine singular:

• el pis desordenat

Other possible forms would be:

• desordenada for feminine singular
• desordenats for masculine plural
• desordenades for feminine plural

Examples:

• La casa està desordenada.
• Els pisos estan desordenats.
• Les habitacions estan desordenades.

Yes. A very common alternative would be:

• Avui el pis està desordenat, i l'he d'endreçar abans de sopar.

Here, l' replaces el pis.

Another possibility, depending on style, is:

• Avui el pis està desordenat i he d'endreçar-lo abans de sopar.

Both are natural. The original sentence is still correct; it is just a bit more repetitive.

Here he is the present tense of haver for I.

In this pattern:

• he de = I have to

This is not the same as English I have meaning possession.

It is part of the obligation structure:

• he de = I have to
• has de = you have to
• ha de = he/she has to
• hem de = we have to
• heu de = you all have to
• han de = they have to

So he d'endreçar means I have to tidy up right now / today / in general present context.