Komšija nas čeka ispred zgrade.

Because some masculine nouns for male people in Serbian end in -a. Komšija means male neighbor, even though its ending may look feminine to an English learner.

So in this sentence:

• komšija = masculine
• it is in the nominative singular
• it is the subject of the sentence

A feminine form would be komšinica.

Because nas means us, while mi means we.

Here, the neighbor is waiting for us, so the pronoun is the direct object of čeka. That means Serbian uses the accusative form:

• mi = we (subject form, nominative)
• nas = us (object form, accusative)

So:

• Mi čekamo. = We are waiting.
• Komšija nas čeka. = The neighbor is waiting for us.

That is a very normal Serbian word order. Object pronouns often appear before the verb in neutral sentences.

So Komšija nas čeka sounds natural and unmarked.

You could also hear other word orders, but they usually change the emphasis:

• Komšija nas čeka. = neutral
• Nas čeka komšija. = stronger focus on us
• Komšija čeka nas. = possible, but more marked or emphatic

Serbian word order is more flexible than English word order.

Čeka is the 3rd person singular present tense form of čekati = to wait.

It agrees with komšija, which is singular:

• ja čekam = I wait / I am waiting
• ti čekaš = you wait
• on/ona čeka = he/she waits
• mi čekamo = we wait
• vi čekate = you wait
• oni čekaju = they wait

So komšija čeka = the neighbor waits / is waiting.

There is no separate word for is here.

In Serbian, the simple present form čeka can often mean either:

• waits
• is waiting

The exact English translation depends on context.

So Serbian does not need a separate auxiliary verb here the way English does in is waiting.

Čekati is imperfective.

That matters because imperfective verbs are the normal choice for:

• ongoing actions
• repeated actions
• general present-time actions

So čeka naturally means something like is waiting or waits.

If Serbian used a perfective verb here, it would give a different feel and usually would not work the same way in an ordinary present-tense statement.

Because the preposition ispred requires the genitive case.

The noun is zgrada = building, and its genitive singular is zgrade.

So:

• zgrada = nominative singular
• zgrade = genitive singular

That is why the sentence says ispred zgrade = in front of the building.

Yes, they are different.

• ispred = in front of
• pred = before / in front of, but it uses a different case and often has a broader meaning

In this sentence, ispred is the natural choice for physical location:

• ispred zgrade = in front of the building

Also, ispred takes the genitive, while pred takes the instrumental.

So you should learn ispred + genitive as a set.

The form zgrade can match more than one grammatical meaning in Serbian, but here the context makes it clear.

It can be:

• genitive singular of zgrada
• nominative plural of zgrada

But after ispred, Serbian requires the genitive, so here it must mean:

• ispred zgrade = in front of the building

not in front of the buildings.

Because Serbian has no articles like English a or the.

So komšija can mean:

• a neighbor
• the neighbor

and zgrada / zgrade can mean:

• a building
• the building

Context tells you which meaning is intended.

That is very normal in Serbian.

Sometimes yes, but not as naturally in this sentence if you want to say exactly who is waiting.

Serbian often allows the subject to be omitted because the verb ending already shows the person and number:

• Čeka nas ispred zgrade. = He/She is waiting for us in front of the building.

But čeka only tells you third person singular. It does not tell you whether the person is the neighbor, a friend, she, he, and so on.

So keeping komšija makes the sentence specific and clear.

Yes. Serbian word order is flexible, and the basic meaning can stay the same while the focus changes.

For example:

• Komšija nas čeka ispred zgrade. = neutral
• Ispred zgrade nas čeka komšija. = stronger focus on the location first
• Nas komšija čeka ispred zgrade. = stronger focus on us

English depends much more on word order for grammar. Serbian uses case endings, so it has more freedom.

A rough pronunciation guide is:

• komšija ≈ KOM-shi-ya
• čeka ≈ CHE-ka
• zgrade ≈ ZGRA-de

Useful letter values here:

• š = sh as in shoe
• č = ch as in chocolate, but usually a bit firmer
• j = y as in yes

So komšija is not pronounced with English j as in job. The j sounds like y.