Kad budemo došli u hotel, prvo ćemo otići na recepciju.

Because Serbian normally uses Future II in a time clause introduced by kad when talking about something that will be completed before another future action.

So the structure is:

• kad budemo došli = when we have arrived / when we arrive
• otići ćemo = we will go

In standard Serbian, kad ćemo doći would usually mean something more like when will we come?, not when we come.

So in this sentence:

• Kad budemo došli u hotel = When we arrive at the hotel
• prvo ćemo otići na recepciju = we’ll first go to the reception desk

It is Future II.

Future II is formed with:

• a future form of biti (budem, budeš, bude, budemo, budete, budu)
• plus the l-participle of the main verb

Here:

• budemo = we will be
• došli = participle of doći (to come / arrive)

Together, budemo došli means something like we will have arrived or, more naturally in English here, when we arrive.

Because Future II does not use the infinitive. It uses the l-participle.

Compare:

• doći ćemo = Future I = we will come
• budemo došli = Future II = when we have come / when we arrive

So:

• doći = infinitive
• došli = participle, needed here for Future II

Because the verb agrees with the subject, which is we.

The hidden subject here is mi = we.

For a mixed group or a group of males, Serbian uses:

• došli = masculine plural

If the group were entirely female, it would be:

• Kad budemo došle u hotel...

If it were singular:

• Kad budem došao... = if the speaker is male
• Kad budem došla... = if the speaker is female

So došli matches the implied we.

Because the second clause is the main future action, so Serbian uses Future I there.

The pattern is very common:

• Kad + Future II in the subordinate time clause
• Future I in the main clause

So:

• Kad budemo došli u hotel = when we arrive
• prvo ćemo otići na recepciju = we will first go to the reception desk

This shows that arriving happens first, and then going to reception happens after that.

Because both actions are seen as single completed events:

• doći = to arrive / come to a destination
• otići = to go away / go off

In this sentence, the speaker is not describing an ongoing process. They mean:

1. we will arrive
2. then we will go to reception

That is why perfective verbs fit naturally here.

Both are in the accusative case because they follow prepositions showing movement toward a destination.

u hotel

• u
  • accusative = motion into / to
• hotel is masculine inanimate, so its accusative looks like its nominative:
  • nominative: hotel
  • accusative: hotel

na recepciju

• na
  • accusative = motion to / onto
• recepcija is feminine:
  • nominative: recepcija
  • accusative: recepciju

So the forms are exactly what you expect for movement.

This is about how Serbian uses prepositions with places.

u hotel

You go into a hotel, so Serbian uses u.

na recepciju

Serbian often uses na for certain destinations, areas, counters, services, events, or institutions. Recepcija is understood as the reception area/desk, so na recepciju is the natural expression.

So even though English often just says to the reception desk, Serbian uses na here.

Kad means when.

Yes, kad and kada usually mean the same thing. The difference is mostly style and rhythm:

• kad = shorter, very common in everyday speech
• kada = slightly fuller or more formal-sounding

So you could also say:

• Kada budemo došli u hotel, prvo ćemo otići na recepciju.

Both are correct.

Because the sentence begins with a subordinate time clause:

• Kad budemo došli u hotel = dependent clause
• prvo ćemo otići na recepciju = main clause

When this kind of clause comes first, Serbian normally separates it with a comma.

So the comma works much like in English:

• When we arrive at the hotel, we’ll first go to reception.

Prvo means first.

Here it modifies the main action:

• prvo ćemo otići na recepciju = we will first go to the reception desk

Its position is fairly flexible, but the given placement sounds very natural. You may also hear:

• Kad budemo došli u hotel, otići ćemo prvo na recepciju.

That still means roughly the same thing, though the original version is smoother and more neutral.

In Serbian, the subject is often omitted because the verb form already shows it.

Here:

• budemo = we form
• ćemo = we will

So mi is understood automatically.

You could include it for emphasis:

• Kad mi budemo došli u hotel, prvo ćemo otići na recepciju.

But normally that would be unnecessary.

Yes. That is usually the most natural English translation.

Although budemo došli is grammatically similar to will have arrived, English normally does not use that form here. English prefers:

• When we arrive at the hotel, we’ll first go to reception.

So the Serbian grammar and the English grammar are not matched word-for-word, even though the meaning is the same.

Yes. In many contexts, otići means to go off / leave, but with a destination it can simply mean go to that place.

Here:

• otići na recepciju = go to the reception desk

It does not sound strange. It just presents the action as a completed move to that location.

Yes, definitely.

A very common alternative would be:

• Kad stignemo u hotel, prvo ćemo otići na recepciju.

Here stignemo comes from stići = to arrive.

This version is often a bit simpler and very natural in everyday speech. The original sentence with budemo došli is also correct; it just uses the clear Future II pattern.

The basic meaning stays the same, but Serbian word order is somewhat flexible.

The original:

• Kad budemo došli u hotel, prvo ćemo otići na recepciju.

Possible variation:

• Prvo ćemo otići na recepciju kad budemo došli u hotel.

That is grammatical, but it changes the rhythm and emphasis. The original version is more natural if you want to set the time frame first: when we arrive at the hotel.

So the word order is not completely fixed, but the given sentence is the most straightforward version.