U dalšího stánku prodávají jogurty, sušenky a sklenice s marmeládou.

Because the preposition u requires the genitive case.

• base form: stánek = stall, stand
• genitive singular: stánku
• adjective další has to match the noun, so it becomes dalšího

So:

• u stánku = at/by the stall
• u dalšího stánku = at/by the next / another stall

This is a very common Czech pattern: preposition + required case.

It can mean either, depending on context.

další often means:

• next / the next one
• another / one more

So u dalšího stánku could mean:

• at the next stall if you are moving from one stall to another
• at another stall if you are just mentioning a different stall

Czech often leaves this kind of nuance to context.

Czech often leaves the subject unstated when it is obvious, unimportant, or meant in a general way.

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

Here it does not necessarily mean a specific known they. It can mean something like:

• they sell
• people are selling
• they’re selling there

In English, we also sometimes use they vaguely, but Czech does this even more naturally.

This is about aspect, which is very important in Czech.

• prodávat = imperfective = to sell, be selling, sell repeatedly / as an activity
• prodat = perfective = to sell completely, to make a sale

In this sentence, the idea is an ongoing activity at a stall, so Czech uses the imperfective verb:

• prodávají = they are selling / they sell

If you used prodají, it would usually mean they will sell or they will manage to sell, because present forms of perfective verbs often have a future meaning.

Grammatically, it is present tense. In English, that can be translated in more than one way depending on context.

So prodávají can mean:

• they sell
• they are selling

In a sentence describing what is happening at a market stall right now, English will often prefer they are selling. But Czech simply uses the present tense and lets context do the work.

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

Here are the base forms:

• jogurt → jogurty
• sušenka → sušenky
• sklenice → sklenice

In this sentence, the accusative plural happens to look the same as the nominative plural for these nouns. That is very common in Czech, especially with inanimate nouns and many feminine nouns.

So even though the forms look like dictionary-style plurals, their job in the sentence is accusative.

On its own, sklenice can mean glasses or glass containers, depending on context.

But in sklenice s marmeládou, the natural meaning is:

• jars with jam
• or simply jars of jam

Because of s marmeládou, we understand that these are not drinking glasses, but containers filled with jam.

So context tells you which English word fits best.

Because the preposition s meaning with takes the instrumental case.

• base form: marmeláda
• instrumental singular: marmeládou

So:

• s marmeládou = with jam

This is another very common Czech pattern:

• s + instrumental

For example:

• s kamarádem = with a friend
• s mlékem = with milk
• s marmeládou = with jam

It describes only sklenice.

So the structure is:

• jogurty
• sušenky
• sklenice s marmeládou

That means:

• yogurts
• biscuits/cookies
• jars with jam

It does not mean that all three things are somehow with jam. Both grammar and meaning strongly connect s marmeládou to sklenice.

Because Czech has no articles.

English needs to choose between:

• a stall
• the stall
• the next stall
• another stall

Czech usually does not mark this with a separate word. Instead, definiteness is understood from:

• context
• word order
• adjectives like další
• sometimes demonstratives like ten

So u dalšího stánku can cover meanings that English splits into several different possibilities.

Yes. Czech word order is much more flexible than English word order.

This sentence begins with U dalšího stánku to set the scene first:

• At the next stall, they sell...

You could also hear something like:

• Prodávají u dalšího stánku jogurty, sušenky a sklenice s marmeládou.

That is grammatical too, but it has a slightly different flow and emphasis.

In Czech, word order often reflects:

• what is already known
• what is being emphasized
• what the speaker wants to highlight first

So the original version sounds very natural for describing a market scene.