Pošto je vani hladno, brzo se presvučem i uzmem debeli džemper.

Here pošto means since or because.

So Pošto je vani hladno means Since it’s cold outside.
This is a conjunction introducing the reason for the action in the main clause.

Be careful: pošto can also mean other things in different contexts, such as after or how much / at what price. In this sentence, though, it clearly means because/since.

Croatian often uses impersonal expressions for weather, temperature, and general conditions.

So:

• Hladno je. = It is cold.
• Vruće je. = It is hot.
• Kasno je. = It is late.

English needs a dummy subject it, but Croatian does not. The verb still appears in 3rd person singular: je.

Vani is an adverb meaning outside or outdoors.

So:

• vani je hladno = it is cold outside

It does not change form for case, gender, or number, because it is an adverb.

You may also hear similar expressions like van or napolju, depending on region and style, but vani is very common.

Because this is an impersonal construction.

In sentences like Hladno je, the word hladno is in the neuter singular form, used for general states or conditions rather than describing a specific noun.

It is not agreeing with a noun like:

• hladan dan = a cold day
• hladna voda = cold water

Instead, it means something like it is cold in a general sense.

Presvučem se comes from presvući se, and it means to change clothes or to get changed.

In this sentence, it suggests changing quickly into something more suitable for the cold.

The se shows that the action is done to oneself. So:

• presvući se = to change one’s clothes / get changed

Without se, the verb would not mean the same thing.

Because se is a clitic, and Croatian clitics usually go in second position in the clause.

Here the beginning of the clause is:

• brzo se presvučem

The first element is brzo, so the clitic se comes right after it.

That is why you get:

• brzo se presvučem

and not:

• brzo presvučem se ← unnatural/wrong in standard word order

If the verb came first, then you would normally say:

• Presvučem se.

This is a question of aspect.

• presvući se, uzeti = perfective
• presvlačiti se, uzimati = imperfective

The perfective forms presvučem and uzmem present the actions as complete whole actions:

• I get changed
• I grab/take a thick sweater

That fits a quick sequence of completed steps.

The imperfective forms would sound more like an ongoing or repeated process:

• presvlačim se
• uzimam

So the perfective forms make the sentence feel more like a complete response to the cold.

Yes, the forms are present tense forms, but with perfective verbs, Croatian present tense often does not mean an action happening literally right now.

Perfective present can be used for things like:

• a future action
• a repeated complete action
• a typical sequence
• vivid narration

So in this sentence, the meaning is something like:

• when it’s cold outside, I quickly get changed and grab a thick sweater
• or since it’s cold outside, I’ll quickly get changed and grab a thick sweater

The exact nuance depends on context.

Because debeli džemper is the direct object of uzmem.

The verb uzeti takes the accusative case.
However, džemper is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• nominative: debeli džemper
• accusative: debeli džemper

That is why the form stays the same.

Not literally.

Uzmem means I take / I grab. So the sentence literally says that the speaker takes a thick sweater.

Because of the context, a listener may naturally assume that the speaker intends to wear it, but the verb itself does not explicitly say put on.

If you wanted to say that more directly, you could use a verb like:

• obučem debeli džemper = I put on a thick sweater

Because Pošto je vani hladno is a subordinate clause placed before the main clause.

Croatian normally separates that kind of introductory clause with a comma:

• Pošto je vani hladno, brzo se presvučem i uzmem debeli džemper.

So the comma marks the boundary between:

• the reason clause: Pošto je vani hladno
• the main clause: brzo se presvučem i uzmem debeli džemper

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

For example, you could also hear:

• Pošto je vani hladno, presvučem se brzo i uzmem debeli džemper.
• Pošto je hladno vani, brzo se presvučem i uzmem debeli džemper.

But the original version sounds natural and smooth.

What matters most is that clitics like se stay in the right position, and that the sentence keeps a natural information flow.