Na trhu dnes prodávají čerstvé jahody a hrozny.

Because na can take different cases depending on meaning.

• na trhu = at the market → location, so trh goes into the locative
• na trh = to the market → direction/movement, so trh goes into the accusative

So here Na trhu means at the market, which is why you see trhu.

The verb prodávají is 3rd person plural: they sell / they are selling.

In Czech, this form is often used with no stated subject to mean something like:

• they
• people
• someone
• they’re selling

So the sentence does not need an explicit oni. It has the same kind of vague subject English sometimes has in They sell fresh strawberries and grapes at the market today.

Depending on context, it could also refer to a specific group of people already known from earlier conversation.

This is a question of aspect.

• prodávají = imperfective → ongoing, repeated, or general selling
• prodají = perfective → completed sale, successful selling, or future completion

In this sentence, the point is that fresh strawberries and grapes are being sold at the market today, so the imperfective prodávají is the natural choice.

If you used prodají, it would suggest something more like they will sell them or they’ll manage to sell them, which is a different idea.

They are the direct objects of prodávají, so they are in the accusative plural.

• jahoda → jahody
• hrozen → hrozny

In these two nouns, the accusative plural looks the same as the nominative plural:

• feminine plural jahody
• masculine inanimate plural hrozny

So even though they are objects, their forms happen to stay the same.

Because the adjective has to agree with the nouns it describes.

Here čerstvé describes both jahody and hrozny, and it matches them in the relevant grammatical features. The ending -é is the correct plural form here and works naturally with:

• čerstvé jahody
• čerstvé hrozny

So čerstvé can modify both nouns together.

Yes, in normal usage it often does.

Strictly speaking:

• hrozen = a bunch/cluster of grapes
• hrozny = bunches/clusters of grapes

But in everyday Czech, hrozny is also commonly used where English would simply say grapes. So in this sentence, it is perfectly natural to understand it as grapes.

Yes, it could.

Czech word order is relatively flexible, and moving dnes changes the emphasis more than the core meaning.

For example:

• Na trhu dnes prodávají...
• Dnes na trhu prodávají...
• Prodávají dnes na trhu...

All of these can work. The version in your sentence sounds natural and fairly neutral. It highlights the setting na trhu first, then adds dnes.

Because Czech has no articles.

English needs words like:

• a / an
• the
• sometimes some

Czech usually does not use separate words for this. Whether something is definite or indefinite is understood from context.

So čerstvé jahody a hrozny can correspond to English expressions like:

• fresh strawberries and grapes
• the fresh strawberries and grapes
• some fresh strawberries and grapes

depending on the situation.

It can do both in principle, because the Czech present tense of an imperfective verb can express:

• a present ongoing action: they are selling
• a habitual/general action: they sell

But here the word dnes strongly points to today, so the most natural reading is about what is being sold today at the market, not a timeless general fact.

No.

With places like market, Czech normally says na trhu, not v trhu.

This is one of those place expressions that you mostly learn as a set phrase:

• na trhu = at the market
• na náměstí = in the square / on the town square
• na poště = at the post office

Even though English often uses in or at, Czech may prefer na with certain locations.