Sve su fino objasnili.

A word-by-word breakdown is:

• Sve = everything / all
• su = are (the 3rd person plural auxiliary used to form the past tense)
• fino = nicely, well, clearly (depending on context)
• objasnili = explained

So the whole sentence means something like:

• They explained everything nicely.
• They explained it all clearly.

It is in the past tense, specifically the perfect tense, which is very common in Croatian.

It is formed with:

• the auxiliary su
• plus the past participle objasnili

So:

• su objasnili = they explained

This is the normal everyday way to say they explained in Croatian.

Because su is a clitic in Croatian. Clitics are short unstressed words that usually go in the second position in the sentence or clause.

Here, the first element is:

• Sve

So the clitic su comes right after it:

• Sve su fino objasnili.

This sounds natural in Croatian.

You could also say:

• Sve su objasnili fino.
• Objasnili su sve fino.

But the placement of clitics follows Croatian word-order rules, not English word order.

Croatian word order is flexible, and moving something to the front often gives it focus or emphasis.

So:

• Sve su fino objasnili.

puts emphasis on everything — as if saying:

• They explained everything clearly.
• They explained it all.

If you said:

• Fino su objasnili sve.

the focus might shift more toward how they explained it.

If you said:

• Objasnili su sve.

that is more neutral.

Here sve means everything or it all.

It is the neuter singular form used in this general sense. Croatian often uses sve to refer to a whole set of things collectively.

So in this sentence, sve is the object of the verb:

• They explained everything.

It does not mean a specific plural noun by itself here, but rather a general everything/all of it.

Objasnili is the past participle form of objasniti (to explain), and it agrees with the subject in number and gender.

Here:

• objasnili = masculine plural (or mixed-gender plural / unspecified plural)

That means the hidden subject is likely:

• they = a group of men, a mixed group, or a group where gender is not being specified

Compare:

• objasnio = he explained
• objasnila = she explained
• objasnili = they explained (masculine/mixed)
• objasnile = they explained (all-female group)

In Croatian, subject pronouns are often left out because the verb form already tells you the person and number.

Here, su objasnili already means:

• they explained

So you do not need to say oni.

If you did say it:

• Oni su sve fino objasnili.

that would usually add emphasis, like:

• They explained everything nicely.

So the subject is understood from the verb.

Not usually in this kind of sentence.

In everyday Croatian, fino often means:

• nicely
• well
• properly
• clearly
  depending on context

So here fino objasniti means something like:

• to explain something nicely
• to explain something clearly
• to explain something well

It is a natural, common expression.

Yes. That is a very natural translation.

Possible translations include:

• They explained everything nicely.
• They explained it all well.
• They explained everything clearly.

The exact English wording depends on context, especially how you want to render fino.

Yes, that is possible, but it may sound slightly different in emphasis.

Compare:

• Sve su fino objasnili. → emphasis on everything
• Objasnili su sve fino. → more neutral, though fino at the end may sound a bit conversational
• Fino su sve objasnili. → emphasis on how well they explained it

Croatian allows several word orders, but they are not always identical in tone or focus.

It is generally neutral and natural.

The word fino can sound a bit:

• conversational
• friendly
• everyday

But the sentence itself is perfectly normal. In a more formal style, someone might choose a word like:

• dobro = well
• jasno = clearly

For example:

• Sve su jasno objasnili. = They explained everything clearly.

Still, Sve su fino objasnili is a very natural sentence in everyday Croatian.