Kada se budim rano, ustajem i otvaram prozor.

Yes. Kada and kad both mean when.

• kada is the full form
• kad is a shorter, very common form in everyday speech

So these are both natural:

• Kada se budim rano, ustajem i otvaram prozor.
• Kad se budim rano, ustajem i otvaram prozor.

The version with kada may sound a little more neutral or slightly more formal, but both are correct.

The verb is buditi se or, in everyday use here, budim se in the present tense meaning to wake up.

The word se is a clitic, and Serbian clitics often go in the second position in a clause. After kada, it is very natural to say:

• Kada se budim rano...

You can also hear:

• Kada budim se rano...

but that sounds unnatural in standard usage.

So in this sentence, se comes right after kada because Serbian likes clitics early in the clause.

Not literally. In many Serbian verbs, se is part of the verb expression and is not translated word-for-word.

Here:

• buditi = to wake someone / to awaken someone
• buditi se = to wake up

So se helps make the verb intransitive or reflexive-like. English uses wake up, while Serbian uses buditi se.

It does not usually mean a strongly emphasized myself in this kind of sentence.

Because Serbian often uses the present tense for habitual or repeated actions.

So:

• Kada se budim rano, ustajem i otvaram prozor.

means something like:

• When I wake up early, I get up and open the window.
• Whenever I wake up early, I get up and open the window.

This is a general habit, not just one event happening right now.

All three are first person singular present tense, so they mean I ...

• budim (se) = I wake up
• ustajem = I get up / I stand up
• otvaram = I open

Serbian usually does not need the pronoun ja because the verb ending already shows the subject.

Because Serbian is a language where the subject pronoun is often omitted when it is already clear from the verb form.

So:

• ustajem already means I get up
• otvaram already means I open

You could add ja:

• Kada se budim rano, ja ustajem i otvaram prozor.

But that would usually add emphasis, contrast, or a special tone. In a normal neutral sentence, leaving out ja is more natural.

This is mainly a question of aspect.

• buditi se / budim se = imperfective
• probuditi se / probudim se = perfective

Very roughly:

• budim se focuses more on the repeated/habitual process
• probudim se often refers to a completed waking-up event

In a sentence about habit, Serbian often prefers the imperfective:

• Kada se budim rano...

But in some contexts, you may also hear:

• Kad se probudim rano...

That can sound more like when I happen to wake up early / when I have woken up early in each individual case. Both can be understandable, but the imperfective fits the routine idea very well.

Again, this is about aspect.

• ustajati / ustajem = imperfective
• ustati / ustanem = perfective

In a habitual sentence, Serbian often uses the imperfective:

• Kada se budim rano, ustajem...

This presents the action as something regular or repeated.

If you used ustanem, it would shift the feel toward a completed single action in each case. That can also appear in some sentence types, but the all-imperfective version here is very natural for describing a routine.

Same basic principle: otvarati is imperfective and otvoriti is perfective.

• otvaram = I open / I am opening / I habitually open
• otvorim = I open in the sense of completing the action once

Because the sentence describes a repeated pattern, otvaram fits well:

• Kada se budim rano, ustajem i otvaram prozor.

It keeps all three actions in the same habitual, imperfective style.

It is in the accusative, but for many masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• prozor = nominative singular
• prozor = accusative singular

That is why after otvaram you still see prozor.

Compare this with a masculine animate noun, where the accusative usually changes:

• vidim čoveka = I see the man

But:

• otvaram prozor = I open the window

Rano is an adverb, meaning early.

It modifies the verb phrase se budim:

• budim se rano = I wake up early

It is not an adjective here. If it were an adjective, it would have to agree with a noun, but there is no noun for it to describe in this sentence.

Yes, Serbian word order is flexible, but not completely free. Some alternatives are possible, though they can sound more or less natural depending on emphasis.

For example:

• Kada se budim rano, ustajem i otvaram prozor. — neutral
• Kada rano se budim... — possible in special contexts, but not the normal choice
• Rano se budim, pa ustajem i otvaram prozor. — different structure, still natural
• Kad se rano budim, ustajem i otvaram prozor. — also natural

The main thing to remember is that se tends to stay near the beginning of its clause.

Because the sentence begins with a subordinate clause:

• Kada se budim rano = dependent clause
• ustajem i otvaram prozor = main clause

When the when-clause comes first, Serbian normally separates it with a comma:

• Kada se budim rano, ustajem i otvaram prozor.

This is very similar to English punctuation in sentences like:

• When I wake up early, I get up and open the window.

It can mean both, depending on context.

In this sentence, the most natural meaning is:

• I get up

because it follows waking up in the morning. In another context, ustajem could also mean I stand up from a chair, bed, etc.

So context tells you which English translation fits best.

It most naturally describes a general habit or repeated situation.

The clues are:

• present tense
• imperfective verbs
• the kada clause introducing a repeated condition

So the meaning is closer to:

• Whenever I wake up early, I get up and open the window

rather than one single event on one particular morning.