Learn Hardcore Croatian: Učiteljica kaže da je to svjetski dan i da svatko može nešto napraviti za zaštitu okoliša. - The teacher says that it is a world day and that everyone can do something for the protection of the environment.

If the teacher is known to be a woman, speakers normally say učiteljica.
If you say učitelj, listeners will imagine a male teacher unless context says otherwise.
Grammatically, you can sometimes use the masculine as a generic term, but in everyday speech, gender is usually marked if it’s known.

What exactly does kaže mean, and what verb is it from?

kaže means (he/she) says.

It is the 3rd person singular present tense of kazati (to say, to tell):

ja kažem – I say
ti kažeš – you say
on/ona/ono kaže – he/she/it says
mi kažemo – we say
vi kažete – you (pl/formal) say
oni/one/ona kažu – they say

In Croatian, both kazati and reći mean “to say”.
You’ll often see kazati in the present (kažem, kažeš, kaže), and reći mostly in compound past tenses (rekao je, “he said”).

What is the function of da in kaže da je to svjetski dan i da svatko može…? Is it like English “that”?

Yes. da here is a subordinating conjunction meaning that.

It introduces a content clause (reported speech / what is being said):

Učiteljica kaže da je to svjetski dan
= The teacher says that it is a world day
…i da svatko može nešto napraviti…
= …and that everyone can do something…

Each da starts a new clause:

da je to svjetski dan
da svatko može nešto napraviti…

You normally repeat da before each clause in such a list.
Leaving out the second da (…svjetski dan i svatko može…) sounds wrong in standard Croatian.

Why is it kaže da je to svjetski dan, not something like kaže da to je svjetski dan?

Croatian word order in subordinate clauses is more rigid than in English.

The normal order here is:

da + verb + (subject/pronoun) + rest

So:

da je to svjetski dan = that it is a world day

Putting to before je (da to je svjetski dan) is possible only in special emphatic or poetic contexts. In neutral, everyday speech, da je to… is the natural order.

What does to do in da je to svjetski dan? Is it just “it”?

Yes, to is a neuter pronoun that often corresponds to English it or this/that, depending on context.

Here it is a dummy subject:

to je svjetski dan = it is a world day / it is World Day

In Croatian, this pattern is very common:

To je knjiga. = That/This is a book.
To je problem. = That is a problem.

So to is required here; you don’t say *je svjetski dan on its own as a full sentence.

Why is svjetski dan in that form? What case and gender is it?

svjetski dan is in the nominative singular masculine:

dan (day) – masculine noun, nominative singular
svjetski (world, global) – adjective, masculine nominative singular, agreeing with dan

Adjectives in Croatian must agree with the noun in:

gender (masculine, feminine, neuter),
number (singular/plural),
case.

So:

svjetski dan – a world day (masc. nom. sg.)
svjetskog dana – of the world day (masc. gen. sg.)
svjetskom danu – to the world day (masc. dat. sg.), etc.

Here it’s a predicate: to je svjetski dan → both to and svjetski dan are in nominative.

What is the difference between svatko and svaki? Why is it svatko može, not svaki može?

Both are related to “every”, but they are used differently.

svatko = everyone / everybody (indefinite pronoun)
- Svatko može nešto napraviti. = Everyone can do something.
svaki = every / each (adjective, must go with a noun)
- Svaki čovjek može nešto napraviti. = Every person can do something.

You cannot say *svaki može nešto napraviti alone (without a noun) in standard Croatian. You must either:

use svatko alone, or
use svaki
- noun (svaki čovjek, svako dijete, etc.).

How does može work with napraviti? Is this like “can do” in English?

Yes. može is the 3rd person singular of moći (can, be able to):

svatko može = everyone can / is able to

When you combine moći with another verb, that other verb appears in the infinitive:

može napraviti = can do / can make
može pomoći = can help
može vidjeti = can see

So svatko može nešto napraviti literally = “everyone can something do” → “everyone can do something”.

What does nešto mean exactly, and where can it go in the sentence?

nešto means something.

In svatko može nešto napraviti, the order is:

svatko (everyone) – subject
može (can) – verb
nešto (something) – object
napraviti (to do) – infinitive

You can also say:

svatko može napraviti nešto

Both are correct. The difference is slight:

nešto napraviti can emphasize the action “do something (at least)”
napraviti nešto is more neutral in focus.

In everyday speech, both orders are very common.

Why is napraviti used here instead of raditi or praviti? What is the aspect?

napraviti is a perfective verb, meaning a completed action: “to do/make (and finish it)”.

Compare:

raditi – to work / to do (ongoing, imperfective)
praviti – to make (ongoing, imperfective; more colloquial/regional in many uses)
napraviti – to make, to do (one-time, completed; perfective)

In this sentence:

nešto napraviti = to do something (concrete, completed action to help the environment)

It suggests a specific, achievable action (plant a tree, recycle something, etc.), not general ongoing activity.

What is going on in za zaštitu okoliša grammatically?

za zaštitu okoliša breaks down as:

za – preposition, here = for
zaštitu – accusative singular of zaštita (protection)
okoliša – genitive singular of okoliš (environment, surroundings)

Structure:

za + accusative → za zaštitu (for protection)
zaštita (protection) čega? (of what?) → okoliša in genitive

So literally:

nešto napraviti za zaštitu okoliša
= to do something for the protection of the environment

This N1 (zaštita) + genitive (okoliša) pattern is very common:

zaštita djece – protection of children
zaštita prirode – protection of nature

Why is it okoliša here and not okoliš?

The dictionary form okoliš is nominative singular.

In the phrase za zaštitu okoliša, okoliša is genitive singular because it depends on zaštita:

zaštita okoliša = protection of the environment

Genitive singular endings for many masculine nouns are -a:

grad → grada (city → of the city)
svijet → svijeta (world → of the world)
okoliš → okoliša (environment → of the environment)

So okoliša is required by the noun zaštita, not by the preposition za (which governs zaštitu, the accusative).