В ресторане сначала подали салат, а потом горячий суп.

Because в ресторане means in the restaurant as a location, not motion toward it.

• в + accusative = motion into somewhere
  
  • в ресторан = into the restaurant / to the restaurant
• в + prepositional = being located somewhere
  
  • в ресторане = in the restaurant

Here the sentence describes what happened while people were already there, so в ресторане is correct.

It means first ... and then ...

• сначала = at first / first
• потом = then / afterward

Together they mark sequence very clearly:

• сначала подали салат = first they served salad
• а потом горячий суп = and then hot soup

This is a very common pattern in Russian for putting events in order.

Russian often uses 3rd person plural with no stated subject to mean they, someone, or people in general.

So подали literally looks like they served, but in English we often translate it more naturally as:

• they served
• the staff served
• salad was served

In this restaurant context, the understood subject is something like the waiters / the staff.

Подали is:

• past tense
• plural
• perfective aspect
• from the verb подать = to serve / hand / bring

So it refers to a completed action: the serving happened as a single finished event.

Подали is perfective because the sentence talks about completed, sequential actions:

• first the salad was served
• then the hot soup was served

Perfective verbs are commonly used for single completed events in a narrative.

If you said подавали, that would be imperfective and would suggest something more like:

• an ongoing process,
• repeated serving,
• or background information.

So here подали is the natural choice.

It is in the accusative, but for many masculine inanimate singular nouns, the accusative looks exactly like the nominative.

• nominative: салат
• accusative: салат

So in the sentence, салат is the direct object of подали, but its form does not visibly change.

The same thing happens with суп:

• nominative: суп
• accusative: суп

Because горячий суп is also a direct object, so it is in the accusative singular.

For masculine inanimate nouns and matching adjectives, accusative singular looks like nominative:

• горячий суп = nominative
• горячий суп = accusative

So after подали, this is exactly the form you expect.

If the noun were animate, the form would often be different.

Russian often omits a repeated verb when it is easy to understand from context.

Full version:

• В ресторане сначала подали салат, а потом подали горячий суп.

Natural shortened version:

• В ресторане сначала подали салат, а потом горячий суп.

The second подали is simply understood. This kind of omission is very common and sounds natural.

Not really in the strong English sense of but.

Russian а can mean several things depending on context. Here it links two stages in a sequence:

• сначала ... а потом ... = first ... and then ...

So in this sentence, а is closer to:

• and then
• while then
• as for what happened next

It does not express a strong contradiction here.

Starting with В ресторане sets the scene first: in the restaurant.

Russian word order is flexible, and putting location first is very natural when you want to establish context before telling what happened.

This order feels like:

• In the restaurant, first they served salad, and then hot soup.

Other word orders are possible, but this one is very normal and clear.

Yes. Сперва and сначала are very close in meaning here, and both can mean first.

For example:

• В ресторане сперва подали салат, а потом горячий суп.

That would also be natural.
In many contexts, the difference is small, and learners can often treat them as near-synonyms.

Russian has no articles like a or the.

So:

• салат can mean a salad or the salad
• горячий суп can mean a hot soup or the hot soup

The exact meaning depends on context. Russian expresses definiteness in other ways, such as context, word order, stress, or additional words.

It can mean both, depending on context.

The verb подать / подавать has the basic idea of handing over, bringing to someone, or serving. In a restaurant, подали is naturally understood as:

• served
• brought out
• brought to the table

So in this sentence, served is the most natural translation, but the broader meaning of the verb is useful to know.