Learn Hardcore Czech: Na hlavním nádraží hledám velkou tabuli, která ukazuje, kdy vlak odjíždí a kdy přijede. - At the main station I am looking for the big board that shows when the train departs and when it arrives.

public buildings or institutions: na poště (at the post office), na univerzitě (at the university)
transport hubs / open areas: na nádraží (at the station), na letišti (at the airport), na náměstí (in the square)

So na (hlavním) nádraží is the standard collocation meaning at the (main) train station.

V nádraží would sound wrong here; it suggests being inside the physical structure of something that isn’t normally used that way.

What case is hlavním nádraží, and why does it look like that?

Hlavním nádraží is in the locative singular (6th case), used after na when it means “at/on” a place.

Breakdown:

nádraží = station, neuter noun
- It’s one of those neuter nouns that look the same in many cases:
  - Nominative sg: nádraží – “a station”
  - Locative sg: nádraží – “(at) the station”
hlavní = main, an adjective
- In the locative singular for neuter nouns, hlavní changes to hlavním:
  - Nominative sg: hlavní nádraží – “the main station”
  - Locative sg: na hlavním nádraží – “at the main station”

So the noun doesn’t change form here, but the adjective does, which tells you it’s locative.

Why is it velkou tabuli and not velká tabule?

Because velkou tabuli is the direct object of hledám (I’m looking for), and direct objects in Czech normally take the accusative case.

tabule = board, display board
- Nominative sg: tabule – “(the) board” (subject)
- Accusative sg: tabuli – “(the) board” (object)
velký = big (adjective)
- Feminine nominative sg: velká tabule – “the big board” (as subject)
- Feminine accusative sg: velkou tabuli – “(for) the big board” (object after hledám)

So:

Velká tabule – “A/The big board is…”
Hledám velkou tabuli – “I’m looking for a big board.”

What exactly does tabule mean here? Is it a “table”, a “sign”, or something else?

In this context, tabule means a (large) information board that shows departure and arrival times.

Rough equivalents in English:

information board
departure board / arrivals board
older style: a physical board, modern: often an electronic display

Related words:

stůl – a table (piece of furniture)
cedule / nápis – a sign (often with text)
displej – a display (electronic)
tabulka – a table (chart, grid), or a small plaque

So velká tabule at a station is the big timetable board, not a piece of furniture.

What is která referring to, and why that form?

Která is a relative pronoun, similar to which / that in English. It introduces the relative clause která ukazuje, kdy vlak odjíždí a kdy přijede (which shows when the train leaves and when it arrives).

It refers back to tabuli:

tabule is feminine singular
in the relative clause, která is the subject (the one that shows something)
Czech relative pronouns must agree in gender and number with the noun they refer to, and take the appropriate case within their clause

So:

feminine singular nominative (as subject) → která

If the noun were masculine or neuter, you’d get:

masculine animate: který
masculine inanimate: který
neuter: které

Why is there a comma before která?

In Czech, a comma is normally used before:

relative clauses starting with který/která/které…
subordinate clauses introduced by conjunctions like že, aby, když, protože, jestli, kdy etc.

Here, která ukazuje, kdy vlak odjíždí a kdy přijede is a relative clause modifying tabuli, so you must write a comma before která.

Why is ukazuje in the present tense if it’s about future train departures and arrivals?

Ukazuje is present tense of ukazovat (to show), but here it doesn’t describe a single moment in time. It describes a general, ongoing function of the board:

(ta tabule) ukazuje… – “(that board) shows…” / “is showing…”

In both English and Czech, present tense can express:

general truths: Voda vaří při 100 °C. – “Water boils at 100°C.”
permanent characteristics: Ten budík zvoní v šest. – “This alarm rings at six.”
scheduled/fixed future events: Vlak odjíždí v 9:00. – “The train leaves at 9:00.”

So která ukazuje, kdy vlak odjíždí a kdy přijede is fine: it’s about what the board regularly/typically shows.

What’s the difference between odjíždí and odjede, and between přijede and přijíždí?

These are aspect pairs – imperfective vs. perfective verbs:

odjíždět (impf.) – to be leaving, to leave (as a repeated or ongoing action)
- odjíždí – “(it) leaves / is leaving / (it) departs”
odjet (pf.) – to leave (a single, completed act)
- odjede – “(it) will leave / will have left”
přijíždět (impf.) – to be arriving, to arrive (repeated/ongoing)
- přijíždí – “(it) arrives / is arriving”
přijet (pf.) – to arrive (one complete event)
- přijede – “(it) will arrive / will have arrived”

In timetables and sentences about schedules you will often see:

either imperfective present: Vlak odjíždí v 9:00, přijíždí v 11:00.
or perfective present with future meaning: Vlak odjede v 9:00, přijede v 11:00.

Both patterns are used; the choice can subtly emphasize different things (habitual vs. single scheduled event).

Why does the sentence use odjíždí but přijede – a mix of aspects?

This combination is possible and not unusual in real speech.

Possible nuance:

kdy vlak odjíždí – a neutral, habitual-sounding form: “what time the train (normally) leaves”
kdy přijede – perfective, focusing on the moment of arrival for this specific journey: “what time it will arrive”

In practice, many speakers don’t think about this contrast very consciously. You could also say:

… kdy vlak odjíždí a kdy přijíždí. (both imperfective)
… kdy vlak odjede a kdy přijede. (both perfective)

All three versions are grammatically correct; the original just happens to mix them in a natural way.

Could I say Hledám na hlavním nádraží velkou tabuli, or does na hlavním nádraží have to go first?

You can change the word order:

Na hlavním nádraží hledám velkou tabuli…
Hledám na hlavním nádraží velkou tabuli…
Hledám velkou tabuli na hlavním nádraží…

All are grammatically correct. The difference is mainly in information structure and emphasis:

Original: Na hlavním nádraží hledám…
→ Sets the location first: “At the main station, I’m looking for…”
Hledám velkou tabuli na hlavním nádraží…
→ Starts with what you’re doing, then adds where.

For a learner, the safest and most neutral options here are the original order or Hledám velkou tabuli na hlavním nádraží.

Why isn’t there any word for “the” in na hlavním nádraží or velkou tabuli?

Czech has no articles (the, a, an). Definiteness and indefiniteness are usually expressed by:

context: Na hlavním nádraží hledám velkou tabuli…
→ In this situation it’s clear there is one specific main station and one specific big board.
word order and stress
demonstratives like ten, ta, to (roughly that/the):
- Hledám tu velkou tabuli. – “I’m looking for that/the big board.”

So:

velkou tabuli can mean a big board or the big board, depending on context.
na hlavním nádraží can mean at a main station or at the main station (usually the, because most cities have one main station).

Do I really need to repeat kdy: kdy vlak odjíždí a kdy přijede? Could I say kdy vlak odjíždí a přijede?

You can omit the second kdy, and it’s grammatically fine:

… která ukazuje, kdy vlak odjíždí a přijede.

Meaning: “which shows when the train leaves and (when it) arrives.”

Repeating kdy:

kdy vlak odjíždí a kdy přijede adds a bit of clarity and balance, and sounds very natural.

Both versions are acceptable. Learners are usually safer keeping the repetition: kdy X a kdy Y.

What does hlavní nádraží mean exactly? Is it a name or just “main station”?

Literally:

hlavní – main, principal
nádraží – station (usually a train station)

So hlavní nádraží = main station / main railway station.

In many Czech cities, Hlavní nádraží is also treated as a proper name for the main central station, e.g.:

Praha hlavní nádraží – Prague Main Station

In your sentence, na hlavním nádraží is in lowercase, used generically: “at the main station (of wherever I am).”