Learn Hardcore Polish: Jutro odbędzie się uroczystość w ratuszu, a potem ciche wesele w domu. - Tomorrow a ceremony will take place at the town hall and then a quiet wedding party at home.

“odbędzie się” sounds a bit more formal and specific: the event is organized and scheduled to take place.
“będzie” is more neutral, just saying that it will exist tomorrow.

So “odbędzie się” is chosen because it fits the idea of an official, planned event (a ceremony, a wedding).

What exactly does the reflexive “się” do in “odbędzie się”?

“Odbyć się” is a reflexive verb used impersonally for events. You almost always see it with “się” when talking about things like:

odbyło się spotkanie – a meeting took place
odbyła się konferencja – a conference took place
odbędzie się uroczystość – a ceremony will take place

You can have “odbyć” without “się”, but then it means to carry out / to perform something, and there is usually a person as the subject:

Odbyli długą podróż. – They made a long journey.
Odbyłem rozmowę z szefem. – I had a talk with the boss.

In the sentence you gave, the focus is on the event happening, not on someone doing it, so the reflexive “odbyć się” is used.

Is “odbędzie się” a future tense form? It looks like present tense.

For perfective verbs in Polish (like “odbyć się”), the present tense forms refer to the future.

odbywać się – imperfective
- odbywa się – it is taking place / takes place (present)
- odbywało się – it was taking place (past)
odbyć się – perfective
- odbędzie się – it will take place (future)
- odbyło się – it took place (past)

So “odbędzie się” looks like a present form but, because the verb is perfective, it means future: will take place.

Why is it “uroczystość” (without any ending) but “w ratuszu” and “w domu” (with -u)?

Different words are in different grammatical cases:

uroczystość – nominative (subject of the sentence)
- Jutro odbędzie się uroczystość.
  Tomorrow (there) will be a ceremony.
w ratuszu, w domu – locative (used after “w” = in, when static, not movement)
- w ratuszu – in the town hall
- w domu – at home / in the house

So:

uroczystość is the thing that will happen (subject → nominative).
w ratuszu, w domu tell you where (location → locative).

Why is it “w ratuszu” and “w domu” and not “w ratusze” or “w domu” vs “w domie”?

Both “ratusz” and “dom” are masculine nouns. In the locative singular, many masculine nouns take the ending -u:

ratusz → w ratuszu – in the town hall
dom → w domu – in the house / at home
sklep → w sklepie – in the shop (here it’s -ie, so you see not all take -u)

You have to learn the locative form with each noun; common masculine patterns:

-u: w domu, w ratuszu, w banku, w parku
-e/-ie: w sklepie, w kinie, w hotelu (again -u), w szpitalu

So “w ratuszu” and “w domu” are just the correct locative forms of those nouns.

Why is it “w ratuszu” and not “na ratuszu”?

In this sentence, “w ratuszu” means inside the building – in the town hall.

w
- locative = inside something:
  - w ratuszu – in the town hall building
  - w domu – in the house

“na ratuszu” would usually mean on the town hall (physically on top) or could sound odd/ambiguous. More natural expressions with “na” are:

na rynku – in the (town) market square
na placu przed ratuszem – in the square in front of the town hall

For an official ceremony taking place inside the building, “w ratuszu” is the normal choice.

What is the nuance of “a potem” here? Could it be just “potem” or “i potem”?

In the sentence:

Jutro odbędzie się uroczystość w ratuszu, a potem ciche wesele w domu.

“a potem” works like “and then”, but “a” often carries a slight contrast or step to the next part:

First: uroczystość w ratuszu (formal, official)
Then, in contrast / as the next stage: ciche wesele w domu (quieter, at home)

Other options:

… potem ciche wesele w domu. – You can drop “a”; it becomes a bit more neutral, just “then”.
… i potem ciche wesele w domu. – Possible, but “i potem” is less common in written style here; “a potem” sounds more natural and stylistically better.

So “a potem” smoothly joins two stages of the day and slightly emphasizes the change from one type of event to another.

Why is there a comma before “a potem”?

In Polish, “a” is a coordinating conjunction that connects two clauses or sentence parts and is usually preceded by a comma.

[Jutro odbędzie się uroczystość w ratuszu], a [potem ciche wesele w domu].

Even though the second part does not repeat the verb (“odbędzie się” is understood), it is still treated as a separate coordinated part, so a comma is needed before “a”.

This is similar to English punctuation with “and then”, but in Polish the comma rule before “a” is more rigid.

Why is it “ciche wesele” and not “cicha wesele”?

Because “wesele” (wedding reception/party) is neuter in Polish.

The adjective must agree in gender, number, and case with the noun:

wesele – neuter, singular, nominative
Neuter nominative singular for “cichy” is “ciche”.

So:

ciche wesele – a quiet wedding reception (correct)
cicha wesele – wrong, because “cicha” is feminine.

Other examples:

ciche mieszkanie – a quiet flat (mieszkanie – neuter)
cicha ulica – a quiet street (ulica – feminine)
cichy dom – a quiet house (dom – masculine)

What’s the difference between “uroczystość” and “wesele” here?

Both can be translated with words connected to “ceremony” or “celebration,” but in Polish wedding vocabulary they are different:

uroczystość w ratuszu – likely the official civil ceremony in the town hall (registry office type event).
- More general: uroczystość = ceremony, solemn event, celebration (not limited to weddings).
wesele w domu – the wedding reception / party at home.
- In Polish:
  - ślub – the wedding ceremony (church or civil, the act of getting married)
  - wesele – the party / reception that follows.

So the sentence describes:
First, the official ceremony in the town hall, then a quiet wedding party at home.

Can I change the word order, for example: “Uroczystość odbędzie się jutro w ratuszu”?

Yes, Polish allows flexible word order, and several variants are correct, with slightly different emphasis:

Jutro odbędzie się uroczystość w ratuszu…
– neutral; tomorrow is at the front, so that time is slightly emphasized.
Uroczystość odbędzie się jutro w ratuszu…
– starts with the ceremony as the topic; feels more like you’re introducing the event first.
W ratuszu jutro odbędzie się uroczystość…
– emphasizes the place first (“In the town hall tomorrow there will be a ceremony…”).

All are grammatical. The original version is very natural and neutral in style.