Dok smo čekali na kolodvoru, otišli smo u čekaonicu jer je svako slobodno sjedalo na peronu bilo mokro.

Dok here means while. It introduces an action that was in progress at the same time as another action.

• Dok smo čekali... = While we were waiting...

In this sentence, waiting is the background action, and otišli smo (we went) is the main event that happened during that time.

Smo is the 1st person plural form of the auxiliary verb biti (to be) used to form the past tense.

So:

• smo čekali = we waited / we were waiting
• smo otišli = we went

Croatian past tense is usually made with:

• a form of biti
  • the past participle

So the structure is:

• mi smo čekali
• mi smo otišli

The subject mi (we) is often omitted because smo already shows who the subject is.

Croatian does not form the past continuous in the same way English does. The form smo čekali can mean:

• we waited
• we were waiting

The exact meaning depends on context.

Here, because of Dok (while), the natural English translation is we were waiting.

Also, čekati is an imperfective verb, which already suggests an ongoing or repeated action, so it works well for were waiting.

Because otišli smo comes from otići, which is a perfective verb meaning to go away / to leave / to go as a completed event.

• ići = to go, to be going
• otići = to go away, to leave, to end up going somewhere

In this sentence, the action is a single completed event: they decided to go into the waiting room. That is why otišli smo is used.

So the contrast is:

• čekali = ongoing background action
• otišli smo = completed action

This is a very typical Croatian aspect pairing.

This is about prepositions and case, especially the difference between location and movement.

1. na kolodvoru

This means at the station.

• na
  • Locative = location
• kolodvoru is the Locative singular of kolodvor

So:

• na kolodvoru = at the station

2. u čekaonicu

This means into the waiting room.

• u
  • Accusative = motion into a place
• čekaonicu is the Accusative singular of čekaonica

So:

• u čekaonicu = into the waiting room

If they were already inside, you would use:

• u čekaonici = in the waiting room

So the sentence contrasts:

• na kolodvoru = location
• u čekaonicu = movement toward/into a place

Because peron (platform) is normally treated as a surface or open area, so Croatian uses na with it.

• na peronu = on the platform

This is similar to many other place expressions in Croatian where English may use in or at, but Croatian prefers na.

Here again, na is followed by the Locative because it describes location:

• peron → peronu

Čekaonicu is Accusative singular.

The basic form is:

• čekaonica = waiting room

Since the sentence expresses motion into the room, Croatian uses:

• u
  • Accusative

That gives:

• u čekaonicu

This is very common with feminine nouns ending in -a:

• soba → u sobu
• škola → u školu
• čekaonica → u čekaonicu

Because all three words must agree with each other in gender, number, and case.

The noun is:

• sjedalo = seat

This noun is:

• neuter
• singular
• here in the nominative

So the words modifying it must also be neuter singular nominative:

• svako = every / each
• slobodno = free, available, unoccupied
• sjedalo = seat

That is why it is:

• svako slobodno sjedalo

If the noun were masculine, it would be different:

• svaki...

If it were feminine:

• svaka...

No. Here slobodno means free in the sense of:

• available
• unoccupied
• not taken

So:

• slobodno sjedalo = a free seat / an available seat

It does not mean free of charge in this sentence.

Sjedalo means seat, often focusing on the sitting place itself.

Possible alternatives would slightly change the meaning:

• sjedalo = seat
• stolica = chair
• klupa = bench

On a platform, sjedalo is a neutral and natural choice if the speaker means any sitting place, not necessarily a separate chair or specifically a bench.

Jer means because. It introduces the reason for the main action.

So:

• otišli smo u čekaonicu = we went into the waiting room
• jer... = because...

The reason is then explained:

• jer je svako slobodno sjedalo na peronu bilo mokro
• because every free seat on the platform was wet

This is a very common point of confusion.

The phrase je bilo mokro is the Croatian way of saying was wet in the past.

Here is how it works:

• je = auxiliary is/has form used to build the past tense
• bilo = past participle of biti
• mokro = wet

So:

• sjedalo je bilo mokro = the seat was wet

Even though English just says was wet, Croatian normally uses this past-tense structure.

This is standard Croatian grammar, not something unusual about this sentence.

Because the subject is sjedalo, and sjedalo is neuter singular.

In Croatian, the past participle and the adjective agree with the noun:

• masculine singular: bio mokar
• feminine singular: bila mokra
• neuter singular: bilo mokro

Since the subject is:

• svako slobodno sjedalo

the correct form is:

• bilo mokro

Croatian often uses svako (every/each) with a singular noun.

So:

• svako sjedalo = every seat
• literally singular, but it refers to all seats one by one

English can do the same:

• every seat was wet

Croatian could also use a plural version, for example:

• Sva slobodna sjedala na peronu bila su mokra.
• All the free seats on the platform were wet.

Both are natural, but the sentence you gave uses the every + singular pattern.

Because Croatian word order is flexible, but short unstressed words like je often come very early in the clause, usually in the so-called second position.

So instead of:

• jer svako slobodno sjedalo je bilo mokro

Croatian more naturally says:

• jer je svako slobodno sjedalo... bilo mokro

This is normal clitic placement in Croatian. English learners often notice it because it does not match English word order.

Both can relate to transport, but they are not always the same.

kolodvor

Usually means a larger station, especially:

• train station
• sometimes bus station

stanica

Often means:

• stop
• station
• a smaller transport point

So in this sentence, kolodvor suggests a main station building/area, which fits well with platform and waiting room.

Yes. In the past tense, Croatian participles agree with the gender and number of the subject.

The sentence has:

• čekali smo
• otišli smo

These forms are used for:

• a group of men, or
• a mixed group

If the group were all female, you would say:

• Dok smo čekale na kolodvoru, otišle smo u čekaonicu...

So the masculine plural form is also the default for mixed groups.

Sometimes dok can have meanings related to while or until, depending on context, but in this sentence it clearly means while.

Because the clause is:

• Dok smo čekali na kolodvoru...

it describes an action in progress during which something else happened. So here there is no ambiguity: while is the correct interpretation.