Razrednica je u dnevnik upisala moje ime i prezime.

Razrednica is a female homeroom teacher / class teacher.
The masculine form is razrednik.

In Croatian, nouns for people often show natural gender, so this word immediately tells you the teacher is female.

That is how the Croatian past tense is normally built:

• a present-tense form of biti = je
• plus the past participle = upisala

So:

• je upisala = she entered / wrote down
• je upisao = he entered / wrote down

This is very common in Croatian:

• Ona je došla. = She came.
• On je došao. = He came.

Because the subject, razrednica, is feminine.

In Croatian past tense, the participle agrees with the subject in gender and number:

• razrednica je upisala = the female teacher entered it
• razrednik je upisao = the male teacher entered it

So the ending -la tells you the subject is feminine singular.

Here upisati means to enter/write something into an official record, register, list, or document.

A rough comparison:

• pisati = to write
• zapisati = to write down, note down
• upisati = to enter into a book/register/form/list

So in this sentence, upisala is especially appropriate because the teacher entered the name into a school record.

Also, upisati is perfective, so it presents the action as completed.

Because after u, Croatian uses:

• accusative for direction/movement into
• locative for location in

Here the idea is entering something into the register, so Croatian uses u dnevnik.

Compare:

• Upisala je ime u dnevnik. = She entered the name into the register.
• Ime je u dnevniku. = The name is in the register.

So:

• u dnevnik = into the register
• u dnevniku = in the register

Not in this context.

Dnevnik can mean things like:

• diary
• journal
• log
• register

In a school sentence like this, it usually means the class register / grade book / official school record book, not a personal diary.

So context matters a lot.

They are in the accusative, because they are the direct object of upisala.

However, both ime and prezime are neuter singular inanimate nouns, and for such nouns the nominative and accusative forms are the same:

• ime → ime
• prezime → prezime

So the case is accusative, even though the form does not visibly change.

Because moje is the neuter singular form of my.

It matches ime:

• moje ime = my name

In moje ime i prezime, the pronoun is understood with both nouns, as if the full version were:

• moje ime i moje prezime

Croatian often avoids repeating the possessive when it is obvious.

So the sentence does not mean that only ime is possessed and prezime is not. It naturally means my first name and surname.

Because moje means my, referring to the speaker.

Svoj/svoja/svoje is a reflexive possessive, used when something belongs to the subject of the sentence.

Here the subject is razrednica, but the name belongs to me, not to her. So:

• moje ime i prezime = my name and surname

If it were the teacher’s own name, Croatian would normally use svoje:

• Razrednica je upisala svoje ime. = The teacher wrote her own name down.

Yes, very much so.

Ime i prezime is a standard Croatian phrase meaning:

• first name and surname
• sometimes effectively full name

You will see it very often on forms and in official language.

For example:

• Upišite ime i prezime. = Enter your name and surname.

Croatian word order is fairly flexible, but not completely free.

This sentence is natural as:

• Razrednica je u dnevnik upisala moje ime i prezime.

You could also hear:

• Razrednica je upisala moje ime i prezime u dnevnik.
• U dnevnik je razrednica upisala moje ime i prezime.

The meaning stays basically the same, but the emphasis changes.

One important point: je is a clitic, and clitics usually stand in the second position of the clause. That is why je appears where it does.

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

So dnevnik can mean:

• a register
• the register

The exact meaning depends on context.

If Croatian wants to be more specific, it can use other words such as demonstratives:

• taj dnevnik = that register
• ovaj dnevnik = this register

But in many normal sentences, no article-like word is needed at all.