Kaput je na stolici, a torba je blizu stolice.

Because Serbian changes noun endings depending on their role in the sentence.

The base form is stolica = chair.

• na stolici = on the chair
  Here, stolica becomes stolici because na is expressing location, so Serbian uses the locative case.

• blizu stolice = near the chair
  Here, stolica becomes stolice because blizu requires the genitive case.

So the noun is the same, but the grammar around it changes its form.

In this sentence, na means on in the sense of location: the coat is located on the chair.

When na expresses location, Serbian usually uses the locative case:

• na stolu = on the table
• na polici = on the shelf
• na stolici = on the chair

So:

• Kaput je na stolici. = The coat is on the chair.

A very important contrast:

• na stolici = on the chair / located there
• na stolicu = onto the chair / movement toward it

So the case changes depending on whether you mean location or motion.

Because blizu is followed by the genitive case in Serbian.

So:

• blizu kuće = near the house
• blizu škole = near the school
• blizu stolice = near the chair

That is why you get stolice, not stolica or stolici, after blizu.

This is something learners usually just have to memorize: certain prepositions and adverbs regularly require certain cases, and blizu takes genitive.

Je means is.

It is the 3rd person singular present tense of biti = to be.

So:

• Kaput je na stolici. = The coat is on the chair.
• Torba je blizu stolice. = The bag is near the chair.

Serbian often uses short unstressed forms like je in normal sentences.

Because there are really two separate clauses:

• Kaput je na stolici
• a torba je blizu stolice

Each clause needs its own verb is, just like in English:

• The coat is on the chair, and the bag is near the chair.

You normally would not leave out the second je here.

A here means something like and, while, or whereas, depending on context.

It connects two ideas and often gives a slight contrast or shift of topic:

• Kaput je na stolici, a torba je blizu stolice.

This feels like:

• The coat is on the chair, and/as for the bag, it is near the chair.
• The coat is on the chair, while the bag is near the chair.

Compare:

• i = simple and
• a = and / while / whereas, often with a mild contrast
• ali = but, stronger contrast

So a is very natural here because the sentence compares the locations of two different objects.

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

So:

• kaput can mean a coat or the coat
• torba can mean a bag or the bag
• stolica can mean a chair or the chair

The exact meaning depends on context.

That means Kaput je na stolici could be understood as:

• The coat is on the chair or
• A coat is on a chair

In real use, context usually makes it clear.

Yes, it matters in Serbian because gender affects adjectives, pronouns, and some endings.

Here the nouns are:

• kaput = masculine
• torba = feminine
• stolica = feminine

In this particular sentence, you mainly notice gender in the noun forms themselves, especially with stolica changing by case.

Later, when you add adjectives, gender becomes even more important:

• crni kaput = black coat
• crna torba = black bag
• crna stolica = black chair

So yes, gender is always part of learning the noun.

Yes, Serbian word order is more flexible than English, but not completely free.

The neutral order here is:

• Kaput je na stolici, a torba je blizu stolice.

You could also hear variations like:

• Na stolici je kaput, a torba je blizu stolice.
• Torba je blizu stolice, a kaput je na stolici.

Changing the order usually changes focus or emphasis, not the basic meaning.

One thing to notice: je is a clitic, so it tends to appear in one of the early positions in the clause, not just anywhere.

A rough pronunciation guide:

• stolica ≈ STO-lee-tsa
• stolici ≈ STO-lee-tsee
• stolice ≈ STO-lee-tseh
• blizu ≈ BLEE-zoo
• torba ≈ TOR-bah
• kaput ≈ kah-POOT

A few useful sound notes:

• c in Serbian is usually like ts in cats
• z is like English z
• vowels are usually clear and short: a, e, i, o, u

So:

• stolici = sto-li-ci with ci sounding like tsee
• stolice = sto-li-ce with ce sounding like tseh

You would usually change the case after na.

• na stolici = on the chair, location
• na stolicu = onto the chair, movement toward the chair

Examples:

• Kaput je na stolici. = The coat is on the chair.
• Stavljam kaput na stolicu. = I am putting the coat onto the chair.

This is a very common Serbian pattern:

• location → often locative
• direction/movement → often accusative

So this sentence is specifically describing where things are, not where they are being moved.

In this sentence, not really. You normally keep it:

• Kaput je na stolici, a torba je blizu stolice.

If you removed stolice, then blizu would be left hanging, because it needs an object:

• blizu čega? = near what?

So blizu cannot stand alone here.

In conversation, Serbian can omit some things when the meaning is obvious, but with blizu, you usually need to say what something is near.