Moja sestra je juče našla kišobran u kancelariji.

It breaks down like this:

• Moja sestra = the subject, my sister
• je našla = the verb phrase, found
• juče = an adverb of time, yesterday
• kišobran = the direct object, umbrella
• u kancelariji = a prepositional phrase showing location, in the office

So the sentence structure is basically:

subject + auxiliary + adverb + main verb + object + location

Serbian word order is more flexible than English, but this is a very natural order.

Because moj changes to match the noun it describes.

Sestra is:

• feminine
• singular
• nominative

So the possessive adjective must also be feminine singular nominative:

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

This kind of agreement is very important in Serbian.

Je is the 3rd person singular present form of biti = to be, and here it is used as an auxiliary verb to make the past tense.

So:

• je našla = has found / found

This is the usual Serbian past tense construction:

• auxiliary biti
• plus the past participle

Examples:

• Ja sam našao / našla = I found
• Ti si našao / našla = you found
• Ona je našla = she found

Because je is a clitic, an unstressed little word that normally goes in the second position in the clause.

In Serbian, second position usually means after the first whole phrase, not necessarily after the first single word.

Here the first phrase is Moja sestra, so the clitic je comes right after it:

• Moja sestra je juče našla kišobran u kancelariji.

You could also say:

• Juče je moja sestra našla kišobran u kancelariji.

Here juče is the first element, so je comes right after that.

Because the past participle in Serbian agrees with the subject in gender and number.

The subject is moja sestra, which is:

• feminine
• singular

So the verb participle must be feminine singular:

• našao = masculine singular
• našla = feminine singular
• našlo = neuter singular
• našli = masculine plural or mixed plural
• našle = feminine plural

Since the subject is she / my sister, našla is correct.

The dictionary form is naći, which means to find.

This verb is a little irregular, so beginners often do not immediately recognize that našla comes from naći.

Some useful forms are:

• naći = to find
• našao = found, masculine singular
• našla = found, feminine singular
• nađe = finds / will find, depending on context

So in this sentence, našla is the feminine past form of naći.

Because it is the direct object in the accusative singular, and for many masculine inanimate nouns, the accusative singular looks exactly the same as the nominative singular.

So:

• nominative: kišobran
• accusative: kišobran

This is normal for masculine inanimate nouns.

Compare:

• Vidim kišobran. = I see an umbrella.
• Kišobran je crn. = The umbrella is black.

Same form, different grammatical role.

Because u can take different cases depending on meaning:

• u + locative = in / inside, location
• u + accusative = into, movement toward the inside

Here the meaning is location, not motion, so Serbian uses the locative:

• u kancelariji = in the office

Compare:

• našla je kišobran u kancelariji = she found the umbrella in the office
• ušla je u kancelariju = she went into the office

So kancelariji is the locative singular form of kancelarija.

Yes. Serbian word order is flexible, and changing it usually changes emphasis rather than core meaning.

For example:

• Moja sestra je juče našla kišobran u kancelariji.
  Neutral, natural statement.

• Juče je moja sestra našla kišobran u kancelariji.
  Emphasizes yesterday.

• Kišobran je moja sestra juče našla u kancelariji.
  Emphasizes the umbrella.

But the clitic je still has to stay in its normal second-position area.

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

So kišobran can mean:

• an umbrella
• the umbrella

The exact meaning depends on context.

The same is true for kancelarija:

• an office
• the office

English requires articles, but Serbian usually leaves that information unstated unless context makes it clear in some other way.

Yes. Naći is a perfective verb.

That matters because perfective verbs present an action as completed, whole, or achieved. In this sentence, the sister successfully found the umbrella, so a perfective verb is a very natural choice.

So:

• našla = found, completed action

An imperfective verb would be used for repeated action, ongoing process, or general description, not for one completed discovery in a simple past event.

So the sentence sounds natural because it describes one finished event:

• yesterday
• she found
• the action is complete

A few pronunciation points that English speakers often ask about:

• j is pronounced like English y
• č is pronounced like ch in church
• š is pronounced like sh in shoe

So approximately:

• juče ≈ YOO-cheh
• kišobran ≈ kee-SHOH-brahn
• kancelariji ≈ kan-tseh-lah-REE-yee

These are only rough English approximations, but they help with the main sounds.