Kad se sutra odjavimo iz hotela, najprije ćemo odnijeti kofere na kolodvor, a onda otići na kratki seminar.

In Croatian, after kad when it means when in a time clause, you normally do not use the future tense the way you often would in English.

So Croatian says:

• Kad se sutra odjavimo iz hotela... = When we check out of the hotel tomorrow...

Even though the action is in the future, Croatian uses a present-form verb of a perfective verb here. This is very common in time clauses.

Using kad ćemo se odjaviti would usually sound unnatural in this kind of sentence.

Odjaviti se is a reflexive verb, meaning to check out or literally something like to unregister oneself.

So:

• odjaviti se = to check out
• odjavimo se = we check out

The little word se is part of the verb. You usually have to learn it together with the verb:

• prijaviti se = to check in / register
• odjaviti se = to check out / unregister

In your sentence, the word order is:

• Kad se sutra odjavimo...

Croatian often places se very early in the clause, usually in second position.

Because Croatian often uses the present tense of a perfective verb to refer to a future completed action, especially in subordinate clauses introduced by words like kad.

Here:

• odjavimo comes from odjaviti se, a perfective verb
• perfective present can refer to a future completed event in clauses like this

So kad se sutra odjavimo means:

• when we have checked out tomorrow
• or more naturally in English: when we check out tomorrow

This is one of the places where Croatian grammar does not line up directly with English tense usage.

Because Croatian often avoids repeating the auxiliary when two future infinitives are coordinated.

So:

• najprije ćemo odnijeti kofere na kolodvor, a onda otići na kratki seminar

means:

• first we will take the suitcases to the station, and then go to a short seminar

The second ćemo is understood:

• najprije ćemo odnijeti..., a onda ćemo otići...

Both versions are possible, but the version without repeating ćemo is very natural and common.

These are time-ordering words.

• najprije = first, first of all
• onda = then, after that

So the sentence is clearly structured:

1. najprije we do one thing
2. onda we do the next thing

This is very common in Croatian for sequencing actions.

Because the preposition iz takes the genitive case.

So:

• hotel = nominative singular
• iz hotela = out of / from the hotel

Other examples:

• iz kuće = from the house
• iz grada = from the city
• iz ureda = from the office

So after iz, you should expect the genitive.

Because kofere is the accusative plural, and it is the direct object of odnijeti.

• koferi = nominative plural = suitcases
• kofere = accusative plural = suitcases as the object

In the sentence:

• odnijeti kofere = to take/carry the suitcases

Since the suitcases are what is being taken, Croatian uses the accusative.

Odnijeti is a perfective verb, while nositi is usually imperfective.

• nositi = to carry / to be carrying / to carry habitually
• odnijeti = to take something away, to carry it off, to bring it somewhere as a completed action

In this sentence, the speaker means a single completed action:

• first we will take the suitcases to the station

That is why odnijeti fits well.

Very roughly:

• nositi kofere = carrying suitcases / being in the process of carrying them
• odnijeti kofere na kolodvor = take the suitcases to the station and complete that action

The preposition na can have several meanings, but in both of these phrases it is followed by the accusative because it expresses movement toward a destination.

• na kolodvor = to the station
• na kratki seminar = to a short seminar

So here na + accusative marks destination.

Compare that with location:

• na kolodvoru = at the station
• na seminaru = at the seminar

So:

• na + accusative = motion to
• na + locative = location at/on

Because after na expressing movement, Croatian uses the accusative, and seminar is a masculine inanimate noun.

So:

• nominative: kratki seminar
• accusative: kratki seminar

For masculine inanimate nouns, nominative and accusative singular are usually the same.

That is why the phrase looks unchanged.

If it were a masculine animate noun, the accusative would look different. But seminar is inanimate, so nominative and accusative match.

Kolodvor usually means a major transport station, especially:

• train station
• bus station in some contexts, depending on region and usage

In practice, if the context is unclear, many learners first understand it as railway station. Croatian can also specify:

• željeznički kolodvor = railway station
• autobusni kolodvor = bus station

So na kolodvor means to the station, but the exact type may depend on context.

This is because se tends to behave like a clitic, and Croatian clitics usually appear very early in the clause, often in second position.

So:

• Kad se sutra odjavimo... sounds natural
• Kad sutra se odjavimo... sounds wrong or very unnatural

Croatian clitic placement is an important part of natural word order. Words like se, ću/ćeš/će, mi, ga, je often follow this pattern.

Yes, you could.

• Kad se sutra odjavimo iz hotela... = When we check out of the hotel tomorrow...
• Nakon što se sutra odjavimo iz hotela... = After we check out of the hotel tomorrow...

The difference is mostly one of nuance:

• kad is simple and very common for time clauses
• nakon što is a bit more explicitly after

Both are correct here, though kad is very natural and economical.

Here a links the two parts of the sentence, but it is not exactly the same as English and in every situation.

In Croatian, a often connects clauses with a mild contrast or a step-by-step progression:

• first this happens, a then that happens

So:

• ..., a onda otići na kratki seminar = ..., and then go to a short seminar

You could think of it as a natural connector between two stages of the plan. It is extremely common in Croatian.