Ovo je zamrznuta hrana.

Because ovo here is a standalone demonstrative pronoun meaning this as in this thing / this here. In that use, Croatian normally uses the neuter singular form.

If you put the demonstrative directly in front of hrana, then it must agree with hrana, which is feminine, so you get ova hrana.

Compare:

• Ovo je zamrznuta hrana. = This is frozen food.
• Ova hrana je zamrznuta. = This food is frozen.

So ovo does not have to match hrana here, because it is not directly modifying it.

Je is the 3rd person singular present form of biti, meaning to be. So it means is.

A useful thing to know is that je is a clitic, so it usually comes in the second position in the sentence:

• Ovo je zamrznuta hrana.

That word order is completely normal.

Because zamrznuta agrees with hrana, and hrana is:

• feminine
• singular
• here in the nominative

Croatian adjectives must agree with the noun they describe in gender, number, and case.

So you get:

• masculine: zamrznut
• feminine: zamrznuta
• neuter: zamrznuto

Since hrana is feminine singular, the adjective must be zamrznuta.

For learners, it is easiest to think of zamrznuta as an adjective-like form meaning frozen.

Historically and grammatically, it comes from a participle related to the verb zamrznuti (to freeze), but in everyday use it behaves like an adjective and agrees with the noun:

• zamrznuta hrana = frozen food
• zamrznuto povrće = frozen vegetables
• zamrznut kruh = frozen bread

So in practical terms, you can treat it like an adjective.

It is in the nominative singular.

That is because after biti (to be), Croatian normally uses the nominative for this kind of sentence:

• Ovo je zamrznuta hrana.

Both zamrznuta and hrana are nominative singular feminine here.

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

So hrana can mean:

• food
• the food
• sometimes some food

The exact meaning depends on the context.

That is very normal in Croatian, and learners have to get used to relying on context instead of articles.

Yes, Croatian word order is fairly flexible, but not every version sounds equally natural in every context.

The most neutral version is:

• Ovo je zamrznuta hrana.

You could also say:

• Zamrznuta hrana je ovo.

But that sounds more marked, like It is frozen food that this is, with special emphasis.

So for normal everyday use, stick with:

• Ovo je zamrznuta hrana.

Yes, but it means something slightly different in structure.

• Ovo je zamrznuta hrana. = This is frozen food.
• Ova hrana je zamrznuta. = This food is frozen.

In the first sentence, zamrznuta hrana is a noun phrase: frozen food.
In the second, zamrznuta is the predicate adjective: is frozen.

Both are correct, but they are not exactly the same sentence.

Yes.

• ovo usually means this (something near the speaker)
• to often means that or sometimes it/that thing, depending on context

So:

• Ovo je zamrznuta hrana. = This is frozen food.
• To je zamrznuta hrana. = That is frozen food.

In real conversation, to is also very common when referring back to something already mentioned.

Yes, there can be.

For food, zamrznuta hrana is the normal and standard way to say frozen food.

Smrznuta can also mean frozen, but it often suggests something being frozen over, very cold, or frozen by the cold. It is not usually the best basic choice for packaged frozen food.

So if you are talking about supermarket-style frozen food, zamrznuta hrana is the safest phrase to use.

A rough pronunciation guide is:

OH-vo ye zamr-ZNOO-ta HRA-na

A few notes:

• j is pronounced like English y
• r in Croatian is a trilled or tapped r
• h is clearly pronounced, unlike in some English words
• zmrz in zamrznuta can feel difficult at first, so it helps to say it slowly: za-mrz-nu-ta

If you want to sound natural, practice it in chunks:

• Ovo je
• zamrznuta hrana

Then put them together.