Kurirska služba je pouzdana.

• kurirska = courier / delivery-related
• služba = service
• je = is
• pouzdana = reliable

So the whole sentence means The courier service is reliable.

Because kurirska is an adjective describing služba, and it has to agree with the noun in gender, number, and case.

Here, služba is:

• feminine
• singular
• nominative

So the adjective also takes the feminine singular nominative form:

• masculine: kurirski
• feminine: kurirska
• neuter: kurirsko

For the same reason: it agrees with služba.

In Serbian, predicate adjectives after to be also match the noun they describe.

So:

• služba = feminine singular
• therefore pouzdana = feminine singular

Compare:

• Kurirski servis je pouzdan. = The courier service is reliable.
  
  • servis is masculine, so kurirski and pouzdan are masculine.
• Kurirska služba je pouzdana.
  
  • služba is feminine, so kurirska and pouzdana are feminine.

In Serbian, most nouns ending in -a are feminine, and služba is one of them.

That means adjectives describing it must also use feminine forms:

• kurirska služba
• dobra služba
• brza služba
• pouzdana služba

There are exceptions to the -a = feminine pattern, but as a beginner, it is a very useful general rule.

Je is the 3rd person singular present form of biti (to be).

Full present tense of biti:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is
• mi smo = we are
• vi ste = you are
• oni/one/ona su = they are

So Kurirska služba je pouzdana literally follows the pattern:

[subject] + [is] + [adjective]

Usually no in a normal present-tense statement like this.

Serbian normally uses the present tense of to be, unlike some languages where it is often omitted.

So:

• Kurirska služba je pouzdana. = correct
• Kurirska služba pouzdana. = generally not correct as a standard sentence

No. Serbian does not have articles like a/an/the.

So Kurirska služba je pouzdana can mean:

• The courier service is reliable
• A courier service is reliable

Which one sounds best depends on context. In many learning materials, it is translated with the because that sounds natural in English.

The main noun phrase kurirska služba is in the nominative, because it is the subject of the sentence.

Also, pouzdana is in the nominative feminine singular because it is a predicate adjective agreeing with the subject after je.

So:

• kurirska = nominative feminine singular
• služba = nominative feminine singular
• pouzdana = nominative feminine singular

Yes, Serbian word order is more flexible than English, but the neutral, most natural order here is:

Kurirska služba je pouzdana.

Other orders are possible for emphasis, for example:

• Pouzdana je kurirska služba.
• Kurirska služba pouzdana je. — possible, but much less natural in ordinary speech

A learner should usually stick with the neutral order: subject + je + adjective

A rough pronunciation is SLOOZH-ba.

A few sound notes:

• ž sounds like the s in measure or vision
• u is like oo in food
• j in Serbian sounds like English y, but there is no j in služba
• žb may feel a little heavy at first, but just say it smoothly: služ-ba

So:

• služba ≈ SLOOZH-ba

Roughly:

• kurirska ≈ koo-REER-ska
• pouzdana ≈ po-ooz-DA-na

Helpful sound notes:

• r is rolled or tapped more than in English
• u = oo
• z is like English z
• dana sounds like DA-na

You do not need perfect stress right away; the important thing is to get the vowel sounds and consonants reasonably close.

Yes. That is also natural and common.

It means basically the same thing:

• kurirska služba = courier service
• kurirski servis = courier service

The grammar changes because servis is masculine:

• kurirski instead of kurirska
• pouzdan instead of pouzdana

So both are correct, but they use different noun genders:

• Kurirska služba je pouzdana.
• Kurirski servis je pouzdan.

It can describe both.

Examples:

• On je pouzdan. = He is reliable.
• Ona je pouzdana. = She is reliable.
• Ovo je pouzdano. = This is reliable.
• Kurirska služba je pouzdana. = The courier service is reliable.

The form changes depending on gender:

• masculine: pouzdan
• feminine: pouzdana
• neuter: pouzdano

The dictionary form of adjectives in Serbian is usually the masculine singular nominative.

So:

• kurirska → dictionary form kurirski
• pouzdana → dictionary form pouzdan

That is the form you would usually look up in a dictionary or vocabulary list.