Learn Hardcore Croatian: U bilježnicu pišem kratke bilješke i primjere iz tečaja. - In the notebook I write short notes and examples from the course.

slightly emphasizes where you write (in the notebook),
sounds very natural and neutral in this context, almost like a topic: “As for in the notebook, that’s where I write short notes and examples from the course.”

Putting pišem first (Pišem u bilježnicu…) is also fine and maybe a bit closer to English-style word order.

So: word order here is flexible and mainly affects emphasis, not meaning or correctness.

Why is it bilježnicu and not bilježnica or bilježnici after u?

The base form is bilježnica (notebook), a feminine noun.

In the sentence, we have u bilježnicu, where bilježnicu is:

accusative singular, feminine

The preposition u can take:

accusative – when there is a direction or movement into something
locative – when something is in/inside a place (static location)

Examples:

Idem u školu. – I am going to school (direction → accusative)
Sam u školi. – I am at school (location → locative)

With pisati u bilježnicu, Croatian usually sees it as “writing into the notebook”, so accusative is used:

u bilježnicu (accusative) – into the notebook

The form bilježnici would be locative (u bilježnici = in the notebook, as a location), but for this common collocation the accusative u bilježnicu is more idiomatic.

So: bilježnicu is accusative singular feminine, required here by u with this meaning.

Why is there no word for my in U bilježnicu pišem…? How would I say in my notebook?

Croatian has no articles (no a, the) and often omits possessive words like my, your when the owner is obvious from context.

In this sentence, it’s normally understood that it’s your own notebook, so Croatian simply says:

U bilježnicu pišem… – I write in (my) notebook

If you really want to emphasize “my notebook”, you can say:

U svoju bilježnicu pišem kratke bilješke i primjere iz tečaja.
(svoju bilježnicu = my own notebook, referring back to ja)

You can also use moju:

U moju bilježnicu pišem…

But in everyday speech, just u bilježnicu is perfectly natural; the my is usually understood.

What form of the verb is pišem, and what is the infinitive? Is there any aspect difference?

Pišem is:

1st person singular, present tense of the verb pisati (to write)
– ja pišem = I write / I am writing

The infinitive is pisati.

Aspect:

pisati is imperfective – it focuses on the ongoing or repeated action:
- I am writing, I (usually) write
The common perfective partner is napisati – to write (and finish writing):

Compare:

Svaki dan pišem bilješke. – I (habitually) write notes.
Danas ću napisati bilješke. – Today I will write the notes (and complete them).

In your sentence, pišem (imperfective) fits well because it describes what you generally or currently do.

Why is there no ja (I) in the sentence? Is it optional?

The subject pronoun ja is normally omitted in Croatian because the verb ending already shows who the subject is.

Pišem kratke bilješke… – I write short notes…
Pišeš kratke bilješke… – You write short notes…
Piše kratke bilješke… – He/She writes short notes…

The -em ending in pišem clearly indicates 1st person singular (ja), so saying Ja pišem… is usually redundant.

You can include ja:

Ja u bilježnicu pišem kratke bilješke…

but that typically adds emphasis, like:

Ja (as opposed to someone else) write short notes in the notebook.

Why is it kratke bilješke? What exactly is kratke agreeing with?

The noun bilješke comes from bilješka (note):

bilješka – note (singular)
bilješke – notes (nominative plural, also accusative plural)

In the sentence, bilješke is a direct object, so it is in the accusative plural.

The adjective kratke (short) changes its form to agree with bilješke in:

gender: feminine
number: plural
case: accusative

So we get:

kratke bilješke – short notes (feminine, plural, accusative)

If it were just one note:

pišem kratku bilješku – I write a short note.
(kratku – feminine, singular, accusative, agreeing with bilješku)

What is the form of bilješke and primjere, and why do they look different?

They are both direct objects, both in accusative plural, but from different noun types:

bilješke
- base form: bilješka (feminine)
- accusative plural: bilješke
- pattern: feminine -a noun → -e in acc. plural
primjere
- base form: primjer (example), masculine
- accusative plural: primjere
- pattern: masculine -er noun → -e in acc. plural (primjer → primjere)

The verb pišem takes both as objects:

pišem kratke bilješke – I write short notes
(pišem) primjere iz tečaja – (I write) examples from the course

So the structure is:

pišem [kratke bilješke] i [primjere iz tečaja]

Does kratke also describe primjere, or only bilješke? If I want to say short notes and (short) examples, is this sentence okay?

Formally, kratke clearly agrees with bilješke (feminine plural).
For primjere (masculine plural), the agreement is not perfect in a strict grammatical sense.

In real-life usage:

Most native speakers will understand kratke bilješke i primjere as:
- short notes and (short) examples
Context helps, and people often “extend” the adjective in their mind to the second noun.

However, if you want to be 100% clear and textbook-correct, especially as a learner, it is better to repeat the adjective:

Pišem kratke bilješke i kratke primjere iz tečaja.
– I write short notes and short examples from the course.

That way there is no doubt that kratke also modifies primjere.

What does iz tečaja mean exactly, and why is tečaja in that form?

iz is a preposition meaning from / out of and it always takes the genitive case.

The noun tečaj (course) is:

nominative singular: tečaj
genitive singular: tečaja

So:

iz tečaja = from the course (from the material/content of the course)

In your sentence:

primjere iz tečaja – examples from the course

Here, tečaja is genitive singular, required by the preposition iz.

Could I use od tečaja or s tečaja instead of iz tečaja? Do they mean the same thing?

They are not exactly the same:

iz tečaja
- literally: from/out of the course
- natural when you talk about content: information, examples, notes taken from the course material or lessons
- fits your sentence best.
s tečaja (or sa tečaja)
- often used for things coming from an event or place:
  - Vratio se s tečaja. – He returned from the course.
- can be used for materials you brought back from a course, but sounds a bit more like “brought back from a course” than “excerpted from course content”.
od tečaja
- sounds unusual in this context and is generally not used to mean “from the course (content)”.

So for examples from the course (material), the most natural choice is precisely:

primjere iz tečaja.