Kad sve završimo, objesit ćemo kapute, sjesti za stol i probati juhu od celera i leće.

Because Croatian normally uses the present tense of a perfective verb after time words like kad when the meaning is future.

So:

• Kad sve završimo = When we finish everything / When we’ve finished everything

Here završimo is the 1st person plural present form of the perfective verb završiti.

For an English speaker, this can feel odd, because English often uses a present form too in time clauses: When we finish everything..., not When we will finish everything.... Croatian works in a similar way here.

Sve means everything or all of it.

In Kad sve završimo, it is the object of završimo, so the phrase means:

• when we finish everything
• when we get everything done

The word order is natural as written. You could also hear Kad završimo sve, but Kad sve završimo is very common and neutral.

Because Croatian usually does not need a subject pronoun when the verb ending already shows who the subject is.

Here:

• završimo = we finish
• ćemo = we will

So mi is unnecessary unless you want emphasis or contrast:

• Mi ćemo objesiti kapute... = We will hang the coats...
  This sounds more emphatic, as if contrasting we with someone else.

This is about how the future tense works in Croatian.

The future is formed with:

• the infinitive
• plus the clitic forms of htjeti: ću, ćeš, će, ćemo, ćete

When the infinitive comes before the auxiliary, an infinitive ending in -ti usually drops its final -i in writing:

• objesiti + ćemo → objesit ćemo

Also, ćemo is a clitic, so it normally cannot stand at the very beginning of the clause by itself. That is why after the comma, starting directly with objesit ćemo is very natural.

You could say Mi ćemo objesiti kapute or Onda ćemo objesiti kapute, because then ćemo is not first.

Because one future form can govern several coordinated infinitives.

So this part:

• objesit ćemo kapute, sjesti za stol i probati juhu...

means:

• we will hang the coats, sit down at the table, and try the soup...

Croatian does not need to repeat ćemo before every infinitive. English works similarly:

• We’ll hang the coats, sit down, and try the soup.

You could repeat it for emphasis or clarity, but normally you do not.

Kapute is the accusative plural of kaput.

It is accusative because it is the direct object of objesiti:

• objesiti kapute = to hang the coats

Useful comparison:

• kaputi = nominative plural
• kapute = accusative plural

So Croatian changes the noun form according to its role in the sentence.

Because sjesti means to sit down, while sjediti means to be sitting / to sit in an ongoing sense.

In this sentence, the actions happen in sequence:

1. finish everything
2. hang the coats
3. sit down at the table
4. try the soup

So sjesti is the right choice because it expresses a completed action: moving into a seated position.

Compare:

• sjesti za stol = to sit down at the table
• sjediti za stolom = to be sitting at the table

With verbs of movement like sjesti, Croatian uses za + accusative to mean to sit down at the table.

So:

• sjesti za stol = to sit down at the table

This is an idiomatic expression. It does not mean physically going behind a table in the English sense.

Compare:

• sjesti za stol = sit down at the table
• sjediti za stolom = be sitting at the table
• na stol = onto the table surface

So na stol would mean something very different, like climbing onto the table.

Here it means try in the sense of taste some food.

Because the object is juhu (soup), the meaning is clearly:

• to try the soup
• to taste the soup

In other contexts, probati can also mean to try to do something:

• Probat ću otvoriti vrata. = I’ll try to open the door.

So the exact English translation depends on the context.

There are two things happening here.

First, juhu is the accusative singular of juha, because it is the direct object of probati:

• probati juhu = to try the soup

Second, od normally takes the genitive case:

• od celera = of/from celery
• od leće = of/from lentils

So:

• celer → celera
• leća → leće

The whole phrase means something like:

• celery and lentil soup
• literally, soup of celery and lentils

Because Kad sve završimo is a subordinate time clause placed before the main clause.

Croatian normally separates that introductory subordinate clause with a comma:

• Kad sve završimo, objesit ćemo kapute...

This is very similar to English punctuation in a sentence like:

• When we finish everything, we’ll hang the coats...

Yes. Kad and kada both mean when.

• Kad sve završimo...
• Kada sve završimo...

Both are correct. Kad is simply the shorter form and is very common in everyday Croatian. Kada can sound a little fuller or slightly more formal, depending on context, but in many situations they are interchangeable.