Moja sestra često kuva pirinač i meso za ručak.

Because moja has to agree with sestra in gender, number, and case.

• sestra is feminine
• singular
• nominative here

So the possessive adjective moj changes to moja.

Compare:

• moj brat = my brother
• moja sestra = my sister
• moje dete = my child

Sestra is in the nominative case because it is the subject of the sentence — the person doing the action.

In this sentence, moja sestra is the one who često kuva, so nominative is used.

Kuva is the 3rd person singular present tense form of the verb kuvati = to cook.

It matches moja sestra, which is equivalent to she.

So:

• ja kuvam = I cook
• ti kuvaš = you cook
• on/ona kuva = he/she cooks

This is a question about aspect, which is very important in Serbian.

• kuvati is imperfective: cooking as a process, or cooking habitually
• skuvati is perfective: to cook something completely, to finish cooking it

Because the sentence contains često = often, it describes a habitual action, so kuva from kuvati is the natural choice.

A perfective verb like skuva would not normally be used for a repeated general habit in this way.

They are in the accusative case because they are the direct objects of kuva — they are the things being cooked.

However, their forms look the same as nominative here:

• pirinač is masculine inanimate, so nominative and accusative are usually the same
• meso is neuter, and nominative and accusative are also the same in the singular

So even though they are accusative, you do not see a form change in this sentence.

Često is an adverb meaning often. In a neutral Serbian sentence, adverbs like this commonly go before the verb:

• Moja sestra često kuva...

That is a very natural word order.

Serbian word order is fairly flexible, so other arrangements are possible, but they can sound more marked or put emphasis in different places. For a learner, subject + često + verb + object is a good basic pattern to remember.

Za ručak literally means for lunch.

The preposition za often takes the accusative case when it means for in this kind of sentence. So:

• za ručak = for lunch
• za večeru = for dinner
• za doručak = for breakfast

Here, ručak is the accusative form. For this noun, the accusative singular happens to look the same as the nominative.

Yes. I simply means and.

Here it connects the two objects:

• pirinač i meso = rice and meat

It works very much like and in English.

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

So:

• sestra can mean a sister, the sister, or simply sister, depending on context
• pirinač can mean rice or the rice
• meso can mean meat or the meat

Context tells you whether something is definite or indefinite.

Č is pronounced roughly like ch in church, but usually a bit firmer.

So:

• često sounds approximately like CHEH-sto
• pirinač ends with a -nach sound, roughly pee-REE-nach

This is different from ć, which is a softer sound. Many learners mix up č and ć at first, so it is good to notice it early.