Ovo su šibice.

Because ovo is the Croatian demonstrative pronoun meaning this / these when you are identifying something.

In Ovo su šibice, ovo works like these are... in English.

A useful distinction is:

• ovo = this / these as a pronoun, often in sentences like This is... / These are...
• ova = a form meaning this / these when it directly modifies a noun

For example:

• Ovo su šibice. = These are matches.
• Ove šibice su nove. = These matches are new.

So here, ovo is correct because it stands on its own before su.

Su is the 3rd person plural form of the verb biti (to be).

So:

• je = is
• su = are

Since šibice is plural, Croatian uses su:

• Ovo je šibica. = This is a match.
• Ovo su šibice. = These are matches.

Šibice is plural here: matches.

The singular form is:

• šibica = match
• šibice = matches

So the pattern is:

• Ovo je šibica.
• Ovo su šibice.

This is why the verb changes from je to su.

The dictionary form is šibica.

That is the singular nominative form, which is the form you normally look up in a dictionary.

From there:

• singular: šibica
• plural: šibice

So if you want to memorize the word, learn it as šibica.

Croatian does not use articles like English a and the.

So šibica can mean:

• a match
• the match

And šibice can mean:

• matches
• the matches

The exact meaning depends on context.

That is completely normal in Croatian, so Ovo su šibice is a full natural sentence without any article.

Here šibice is in the nominative plural.

That is because it is the predicate noun in an identification sentence with to be:

• Ovo je knjiga.
• Ovo su ključevi.
• Ovo su šibice.

A learner does not need to overthink it at first: after this kind of This is... / These are... structure, Croatian normally uses the nominative form.

A simple pronunciation guide is:

• Ovo ≈ OH-vo
• su ≈ soo
• šibice ≈ SHEE-bee-tseh

A few key points:

• š sounds like sh in shoe
• c in Croatian usually sounds like ts in cats
• Stress can vary by dialect and teaching style, but for a beginner the approximation above is good enough

So the whole sentence sounds roughly like:

OH-vo soo SHEE-bee-tseh

Yes, To su šibice is also possible and very common.

Both ovo and to can appear in identifying sentences, but they are not exactly the same in feel:

• ovo = this / these here
• to = that / those or sometimes a more general that / those are

Very roughly:

• Ovo su šibice. = These are matches.
• To su šibice. = Those are matches. or Those are matches / They are matches.

In real usage, both can appear in similar contexts, but ovo usually feels closer to the speaker.

Because Croatian often uses ovo in identification sentences where English uses these.

English changes:

• This is...
• These are...

Croatian often keeps ovo and lets the verb show whether the thing is singular or plural:

• Ovo je šibica.
• Ovo su šibice.

So the singular/plural difference is shown mainly by:

1. je / su
2. the noun form (šibica / šibice)

That may feel unusual to an English speaker, but it is a normal Croatian pattern.

Yes, Croatian word order is more flexible than English, but Ovo su šibice is the most neutral and natural version.

You may also hear:

• Šibice su ovo.

But that sounds marked or contrastive, as if you are emphasizing matches specifically.

For learners, the safest default is:

• Ovo su šibice.

Šibica usually means a matchstick, and šibice means matches.

Depending on context, people may sometimes use the plural in a practical sense when talking about a box of matches, but the literal word is still matches, not specifically matchbox.

If you want to be precise:

• šibica = a match
• šibice = matches
• kutija šibica = a box of matches