Baka navečer čita bajku o zmaju koji živi u velikoj šumi.

Because bajku is the direct object of the verb čita (reads).

The basic noun is bajka (fairy tale). In this sentence, it changes to the accusative singular:

• bajka = nominative singular
• bajku = accusative singular

So:

• Baka čita bajku. = Grandma is reading a fairy tale.

This is very common with feminine nouns ending in -a:

• žena → ženu
• knjiga → knjigu
• bajka → bajku

Navečer means in the evening or during the evening.

It is an adverb, so it does not change form. In this sentence it tells us when the action happens:

• Baka navečer čita... = Grandma reads... in the evening

A learner might expect something more literal like u večeri, but Croatian normally uses navečer for this idea.

Compare:

• ujutro = in the morning
• popodne = in the afternoon
• navečer = in the evening
• noću = at night

Because the preposition o requires the locative case when it means about.

The noun zmaj (dragon) therefore changes to locative singular:

• zmaj = nominative
• zmaju = locative

So:

• bajka o zmaju = a fairy tale about a dragon

This pattern is important:

• pričati o prijatelju = to talk about a friend
• razmišljati o poslu = to think about work
• čitati o gradu = to read about a city

Koji means who, which, or that in a relative clause.

Here it refers back to zmaju (dragon) and introduces extra information about it:

• o zmaju koji živi u velikoj šumi
• about a dragon that lives in a big forest

Even though zmaju is in the locative after o, the pronoun koji is in the nominative because it is the subject of the verb živi.

So inside the relative clause:

• koji živi = who lives / that lives

Because the case of koji depends on its job inside the relative clause, not just on the noun it refers to.

In:

• o zmaju koji živi u velikoj šumi

zmaju is locative because it follows o.

But in the clause:

• koji živi u velikoj šumi

the word koji is the subject of živi, so it must be nominative.

This is a very important idea in Croatian grammar: relative pronouns agree with the noun in gender and number, but their case depends on their function in the relative clause.

Because u can take different cases depending on meaning.

Here, u velikoj šumi means in a big forest, describing a location, not movement. So Croatian uses the locative:

• šuma = forest
• u šumi = in the forest
• u velikoj šumi = in the big forest

The adjective also has to agree with the noun:

• velikoj matches šumi
• both are feminine singular locative

If there were movement into the forest, Croatian would normally use the accusative:

• ide u veliku šumu = he/she is going into the big forest

Not necessarily. In Croatian, the present tense can describe:

• something happening right now
• a habit
• a general fact

So:

• Baka navečer čita... can mean Grandma reads in the evening as a habit
• or, depending on context, Grandma is reading in the evening

Likewise:

• zmaj koji živi u velikoj šumi = a dragon that lives in a big forest

That sounds like a general characteristic of the dragon.

Because Croatian has no articles.

English says:

• the grandmother
• a fairy tale
• the dragon
• a big forest

Croatian simply uses:

• baka
• bajku
• zmaju
• velikoj šumi

Whether something is definite or indefinite is usually understood from:

• context
• word order
• stress
• the general situation

So bajku could correspond to a fairy tale or the fairy tale, depending on context. In this sentence, English naturally uses a fairy tale.

Yes. Croatian word order is fairly flexible because case endings show grammatical roles.

The sentence:

• Baka navečer čita bajku o zmaju koji živi u velikoj šumi.

is a neutral, natural order.

But other orders are possible, depending on emphasis:

• Navečer baka čita bajku o zmaju...
• Bajku o zmaju baka čita navečer.

These do not necessarily change the basic meaning, but they can change focus or style.

For learners, the given order is a good standard pattern:

• subject + time expression + verb + object

Baka most commonly means grandmother or grandma.

Depending on context, it can sound:

• neutral: grandmother
• warm/familiar: grandma

In everyday Croatian, family words often work a little differently from English. For example, Croatian may omit possessives where English prefers them. So:

• Baka čita... may naturally mean Grandma is reading...
• even without explicitly saying my grandma

Because of the form of koji and the logic of the sentence.

The noun zmaj is masculine singular, and koji is also masculine singular nominative. It agrees with zmaj.

The noun bajka is feminine, so if the relative clause referred to bajka, you would expect koja, not koji.

So:

• bajka o zmaju koji živi... = a fairy tale about a dragon that lives...
• bajka koja govori o zmaju... = a fairy tale that talks about a dragon...

This agreement helps Croatian show exactly what is being described.

A few words may stand out:

• čita: č is like ch in church, but usually crisper
• bajku: j is pronounced like English y
• zmaju: again, j sounds like y, so roughly ZMA-yu
• šumi: š sounds like sh
• živi: ž sounds like the s in measure or zh

Also, Croatian spelling is very regular, so once you know the sound of each letter, pronunciation becomes much easier than in English.

Because this is a restrictive relative clause: it identifies which dragon we mean.

• zmaj koji živi u velikoj šumi = the dragon that lives in the big forest

In Croatian, commas are generally not used before restrictive relative clauses like this.

A comma would suggest a more added, parenthetical comment, which is not the idea here. The clause is essential to the description of the dragon.