Poslije posla sjest ćemo na klupu u parku.

Because poslije (after) requires the genitive case.

• posao = job/work (dictionary form, nominative)
• posla = genitive singular

So:

• poslije posla = after work
• literally: after of-work

This is a very common pattern in Croatian:

• poslije škole = after school
• poslije ručka = after lunch
• poslije sastanka = after the meeting

Posla is genitive singular of posao.

The noun posao is a masculine noun, and its genitive singular form is irregular-looking for English speakers because the base changes a little:

• nominative: posao
• genitive: posla

So in the sentence:

• Poslije posla = After work

You do not need a preposition meaning the or a, because Croatian has no articles.

This is the future tense.

The basic infinitive is:

• sjesti = to sit down

When the future auxiliary comes after the infinitive, standard Croatian usually drops the final -i of the infinitive:

• sjesti + ćemo → sjest ćemo

So:

• sjest ćemo = we will sit down

Compare:

• Mi ćemo sjesti. = We will sit down.
• Sjest ćemo. = We will sit down.

Both express the future, but the form changes depending on word order.

Because sjesti means to sit down or to take a seat, while sjediti means to be sitting.

That is an aspect difference:

• sjesti = perfective, one completed action
• sjediti = imperfective, ongoing state

In this sentence:

• Poslije posla sjest ćemo na klupu u parku.
• After work, we’ll sit down on a bench in the park.

The idea is that we will sit down, not that we are already in the state of sitting.

Compare:

• Sjest ćemo na klupu. = We’ll sit down on the bench.
• Sjedit ćemo na klupi. = We’ll be sitting on the bench.

Because Croatian uses different cases depending on whether there is movement toward a place or location at a place.

Here, sjesti na klupu means to sit down onto the bench, so there is movement toward the bench. That is why Croatian uses the accusative:

• klupa = bench
• na klupu = onto the bench

Compare:

• sjesti na klupu = to sit down on/onto the bench
• sjediti na klupi = to sit on the bench / to be sitting on the bench

So:

• na klupu = destination
• na klupi = location

This is a very important pattern in Croatian.

Klupu is the accusative singular of klupa.

• nominative: klupa = bench
• accusative: klupu

It is accusative because the phrase na klupu expresses movement toward a destination.

So in the sentence:

• sjest ćemo na klupu = we will sit down on/onto a bench

Because u parku expresses location, not movement.

The bench is located in the park, so Croatian uses u + locative:

• park = park
• u parku = in the park

Compare:

• ići u park = to go into the park → movement, so accusative
• biti u parku = to be in the park → location, so locative

In your sentence, the action of sitting is aimed at the bench (na klupu), while u parku simply tells you where that bench is.

Parku is the locative singular of park.

• nominative: park
• locative: parku

It appears after u when u means in in a location sense:

• u parku = in the park
• u školi = in school
• u kući = in the house

Because Croatian does not have articles like English a/an/the.

So:

• na klupu can mean onto a bench or onto the bench
• u parku can mean in a park or in the park

Which meaning is intended depends on context.

In many learning examples, English uses a or the, but Croatian simply leaves that information unstated unless something else in the sentence makes it clear.

No. Croatian also commonly uses nakon.

So you could also say:

• Nakon posla sjest ćemo na klupu u parku.

That means essentially the same thing: After work, we’ll sit down on a bench in the park.

A learner should know:

• poslije is very common in everyday speech
• nakon is also very common and can sound a bit more formal or neutral depending on context

Both normally take the genitive.

Croatian word order is more flexible than English word order.

The sentence starts with Poslije posla to set the time frame:

• After work, ...

That is very natural. Croatian often puts time expressions near the beginning of the sentence.

Then:

• sjest ćemo = we will sit down
• na klupu = on/onto a bench
• u parku = in the park

So the structure is roughly:

• time
  • verb
    • destination
      • location

Other word orders are possible too, depending on emphasis, for example:

• Sjest ćemo na klupu u parku poslije posla.
• Na klupu u parku sjest ćemo poslije posla.

But the original sentence is the most neutral and natural.

No. Croatian usually does not need the subject pronoun if the verb already makes the subject clear.

• sjest ćemo already means we will sit down

So:

• Sjest ćemo na klupu u parku. = We’ll sit down on a bench in the park.

You could add mi for emphasis or contrast:

• Mi ćemo sjesti, a oni će ostati stajati.
• We will sit down, but they will remain standing.

Without emphasis, leaving mi out is more natural.

A rough pronunciation guide is:

• sjest ćemo ≈ syest che-mo

A few helpful points:

• sj sounds like a soft sy
• ć in ćemo is a soft sound, often approximated for English speakers as ch, though it is not exactly the English ch
• č and ć are different sounds in Croatian, though many learners take time to hear and produce the difference

So don’t worry if it feels difficult at first: sjest ćemo is a perfectly normal cluster for Croatian, but it can be awkward for English speakers.

Yes. That is just a different English wording of the same Croatian sentence.

Croatian does not force exactly the same word order or article choices as English, so several English translations are possible:

• After work, we’ll sit down on a bench in the park.
• We’ll sit down on a bench in the park after work.
• After work, we’ll sit on the bench in the park.

The exact English choice depends on context, especially whether a bench or the bench is intended. The Croatian sentence itself leaves that open unless the wider context makes it specific.