Sezónní zelenina je na tržním stánku.

In Czech, zelenina is usually a collective/uncountable noun, so it often works like vegetables or produce in English.

So:

• zelenina je... = the vegetables / the produce is...
• It takes a singular verb, so je is correct.

If you use the plural zeleniny, it usually means different kinds/types of vegetables, not just vegetables in general.

It is in the nominative case, because it is the subject of the sentence — the thing being talked about.

• zelenina = nominative singular
• sezónní matches zelenina in gender, number, and case

So sezónní zelenina means seasonal vegetables / seasonal produce as the subject of the sentence.

Je is the 3rd person singular present tense of být (to be).

So:

• je = is

It connects the subject with the location:

• Sezónní zelenina je na tržním stánku.
• The seasonal vegetables are at/on the market stall.

Even though English uses are with vegetables, Czech uses je because zelenina is grammatically singular.

Both na and v can sometimes translate as in/at/on, but they are used differently.

Here, na stánku usually means:

• at the stall
• on the stall
• at the vendor’s stand

It refers to the stall as a sales point / place of business.

By contrast, v stánku would mean more literally:

• in the stall
• inside the booth

So in this sentence, na tržním stánku is the natural choice if you mean the vegetables are being sold or displayed there.

Because na can take different cases depending on the meaning:

• na + locative = location (on / at)
• na + accusative = movement toward something (onto / to)

Here the sentence describes where something is, not where it is going, so Czech uses the locative:

• na tržním stánku = at/on the market stall

Compare:

• Je na tržním stánku. = It is at the stall.
• Jde na tržní stánek. = He/she is going to the stall.

Because the adjective has to agree with stánku in:

• gender
• number
• case

stánek is:

• masculine inanimate
• singular
• here in the locative

So the adjective also has to be masculine singular locative:

• dictionary form: tržní
• in this sentence: tržním

This is normal adjective agreement in Czech.

Because after na with a location meaning, the noun goes into the locative case.

The base form is:

• stánek = stall, stand

But in the locative singular, it becomes:

• na stánku = at/on the stall

So:

• stánek = nominative
• stánku = locative

This kind of noun change is very common in Czech after prepositions.

Yes. Czech word order is more flexible than English.

The sentence:

• Sezónní zelenina je na tržním stánku.

is a perfectly normal neutral version.

But you could also say:

• Na tržním stánku je sezónní zelenina.

This puts more focus on the location first, something like:

• At the market stall, there are seasonal vegetables.

So the meaning stays basically the same, but the emphasis changes.

A rough pronunciation for an English speaker is:

SEH-zoh-nyee ZEH-leh-nih-na yeh na TRZH-neem STAHN-koo

A few useful notes:

• Czech stress is usually on the first syllable of each word.
• ž sounds like the s in measure.
• í is a long ee sound.
• á is a long ah sound.
• In tržním, the ň sound is like ny in canyon.

So:

• Sezónní ≈ SEH-zoh-nyee
• zelenina ≈ ZEH-leh-nih-na
• je ≈ yeh
• tržním ≈ TRZH-neem
• stánku ≈ STAHN-koo

Yes, it is a very natural combination.

• tržní = market-related
• stánek = stall, stand, booth

So tržní stánek means market stall or market stand.

You may also see similar expressions like:

• stánek na trhu = a stall at the market

But tržní stánek is a normal, idiomatic way to say it.