Ordinea serviciului se schimbă după set.

Because ordinea is the definite form of ordine.

• ordine = order
• ordinea = the order

Romanian usually puts the definite article at the end of the noun instead of using a separate word like English the.

So:

• ordine = order
• ordinea = the order

In this sentence, we are talking about a specific thing: the service order.

Serviciului is the form meaning of the service.

Here, Romanian is expressing a relationship similar to English the order of the service. That relationship is often shown with the genitive.

Breakdown:

• serviciu = service
• serviciul = the service
• serviciului = of the service / to the service

So:

• ordinea serviciului = the order of the service

This is a very common Romanian pattern:

• cartea elevului = the student's book / the book of the student
• culoarea mașinii = the car's color / the color of the car

Yes, it is the same basic word, but the meaning depends on context.

Serviciu can mean several things, including:

• service
• job / work
• in sports, serve / service

In a sports context, serviciul often refers to the serve or service.

So in this sentence, ordinea serviciului means the order in which players serve.

Se schimbă means changes or is changed, depending on context.

The base verb is:

• a schimba = to change

In this sentence, the form se schimbă is very common in Romanian for things that happen by themselves, generally, or in a more impersonal/passive-like way.

So:

• Ordinea serviciului se schimbă = The service order changes / The service order is changed

In rule-style language, English often says is changed, while Romanian often uses se + verb.

Compare:

• Ușa se deschide. = The door opens / is opened.
• Programul se modifică. = The schedule changes / is changed.

Grammatically, it uses the reflexive particle se, but here it does not mean a literal reflexive action like he washes himself.

Instead, se schimbă is one of those very common Romanian structures where se gives a meaning like:

• something happens in general
• something changes on its own
• something is changed in an impersonal way

So it is best to understand it here as:

• changes
• or is changed

rather than literally changes itself, even though that is the historical structure behind it.

Because Romanian often leaves a noun without the definite article after a preposition when speaking in a general, rule-like, or category-based way.

So:

• după set = after the set / after a set / after each set, depending on context

In sports rules, this kind of wording can sound natural and general.

If you say după setul, that usually needs more information after it, for example:

• după setul al doilea = after the second set
• după setul decisiv = after the deciding set

So in your sentence, după set has a general rule-book feel.

Yes. Romanian word order is fairly flexible.

The original sentence:

• Ordinea serviciului se schimbă după set.

A natural alternative would be:

• După set, ordinea serviciului se schimbă.

Both are correct. The difference is mostly about emphasis:

• Ordinea serviciului... puts focus first on the service order
• După set... puts focus first on when the change happens

The original version is neutral and perfectly natural.

A rough pronunciation guide for an English speaker is:

OR-dee-nya ser-VEE-chee-oo-luy se skhim-BUH DOO-puh set

A few useful details:

• ordinea: the ni sounds like ny in canyon
• serviciului: this is the trickiest word; the ending -ului is roughly oo-luy
• schimbă: sch here sounds like skh, not like English sh
• după: the final ă is a short central vowel, something like a relaxed uh

Here are the dictionary forms:

• ordinea ← ordine = order
• serviciului ← serviciu = service / serve
• se schimbă ← a se schimba or a schimba = to change
• după = after
• set = set

So the sentence is built from very common Romanian patterns: a noun with a definite article, a genitive noun, a se verb, and a simple prepositional phrase.

Because Romanian normally puts the possessor or of-phrase after the main noun.

So:

• ordinea serviciului = the order of the service

This is the normal Romanian structure.

English can use either:

• the order of the service
• the service order

Romanian usually prefers the equivalent of the order of the service in this kind of phrase.

It sounds natural, especially in:

• sports rules
• instructions
• formal explanations
• commentary about how a game works

It has a slightly rulebook/instructional tone rather than casual conversation, but it is completely normal Romanian.

In a very casual spoken explanation, someone might rephrase it depending on the sport and context, but the sentence itself is standard and correct.