U kampu smo upoznali ženu koja svako ljeto pravi roštilj i uvijek nosi dovoljno ugljena.

Because u means in or at when it expresses location, and with a location meaning it takes the locative case.

• kamp = camp / campsite
• u kampu = in the camp / at the campsite

So kamp changes to kampu because it is singular locative. If u meant motion into somewhere, it would normally take the accusative instead.

Croatian often drops subject pronouns when they are already clear from the verb form.

• smo = we are as an auxiliary, here used to form the past tense
• upoznali smo = we met

So Croatian does not need mi unless you want emphasis:

• Upoznali smo ženu = We met a woman
• Mi smo upoznali ženu = We met a woman, with extra emphasis on we

Also, smo is a clitic, so it usually appears in the second position of the clause. That is why U kampu smo upoznali... sounds natural.

Upoznati means to meet or to get to know someone, usually as a completed event. It is the natural verb here because the sentence refers to one completed past action: meeting the woman.

So:

• upoznali smo = we met / we got to know

This is different from verbs like:

• znati = to know
• poznavati = to know, be acquainted with

A native English speaker often expects one verb to cover both meet and know, but Croatian separates those ideas more clearly.

Because ženu is the accusative singular of žena.

Here, ženu is the direct object of upoznali smo:

• žena = woman, nominative
• ženu = woman, accusative

For many feminine nouns ending in -a, the accusative singular ends in -u:

• žena → ženu
• kuća → kuću
• sestra → sestru

Because koja is the subject inside the relative clause.

In ženu koja svako ljeto pravi roštilj..., the word koja refers back to ženu, but its case is determined by its role in the relative clause, not by the case of ženu in the main clause.

Inside the clause:

• koja pravi roštilj
• koja nosi dovoljno ugljena

Here koja is the one doing the actions, so it must be nominative.

Compare:

• ženu koja pravi roštilj = the woman who makes barbecue
• ženu koju smo upoznali = the woman whom we met

So koja = subject, koju = object.

Because the relative clause describes the woman’s usual habit or general characteristic, not just what she was doing at that one past moment.

So the sentence means something like:

• We met a woman who every summer makes barbecue and always brings enough charcoal

The meeting happened in the past, but her behavior is presented as something generally true about her.

This is very natural in Croatian. English does something similar:

• We met a woman who always brings enough charcoal

Even though met is past, brings is still present because it describes her regular behavior.

Here svako ljeto is an adverbial time expression meaning every summer.

Formally, it is the accusative singular:

• svako = every, neuter singular accusative/nominative
• ljeto = summer, neuter singular

Croatian often uses the accusative for certain time expressions.

You may also see svakog ljeta, which is also common and also means every summer. So both patterns exist:

• svako ljeto
• svakog ljeta

In this sentence, svako ljeto is perfectly natural.

Literally, praviti means to make, and roštilj can refer to:

• a grill
• grilled food
• a barbecue

In this sentence, praviti roštilj means something like to make / prepare / have a barbecue.

It is a normal everyday expression. Croatian often uses praviti where English might use make, do, or even have, depending on the context.

Because after words expressing quantity or amount, Croatian usually uses the genitive.

• dovoljno = enough
• ugljen = charcoal / coal
• ugljena = genitive singular

So:

• dovoljno ugljena = enough charcoal

This is the same pattern as:

• puno vode = a lot of water
• malo vremena = little time
• dovoljno novca = enough money

Since ugljen is being treated as a mass noun here, the singular genitive is natural.

Yes, Croatian word order is fairly flexible, but some parts still have strong tendencies.

A few important points here:

• smo is a clitic, so it usually goes in second position
• the relative clause normally comes after the noun it describes: ženu koja...
• uvijek can move around somewhat, but uvijek nosi is very natural

So:

• U kampu smo upoznali ženu... sounds natural and emphasizes the setting first
• You could also say Upoznali smo ženu u kampu..., but the focus feels a little different

The sentence you have is a very normal Croatian word order.

Croatian has no articles, so it does not directly mark a versus the the way English does.

That means ženu can mean:

• a woman
• the woman

Context decides.

In this sentence, English would usually say a woman, because she is being introduced for the first time. But Croatian itself does not force that choice.

This is one of the biggest differences for English speakers learning Croatian.

The past participle in Croatian agrees with the subject in gender and number.

Here the subject is an implied we, and the form used is:

• upoznali = masculine plural

This is the default plural form for:

• a group of men
• a mixed group
• an unspecified we

If the speakers were all female, it would be:

• U kampu smo upoznale ženu...

So the form tells you something about the speakers, even though the pronoun is not stated.