Stvar je nekorišćena.

Here stvar means thing, item, or object.

It is a very broad word in Serbian, just like thing in English. In other contexts, stvar can also mean matter, issue, or affair, but in Stvar je nekorišćena, it most naturally refers to a physical item.

Also, stvar is a feminine noun.

Because Serbian has no articles.

So stvar can mean:

• a thing
• the thing
• this item
• that item

The exact meaning depends on context.

If Serbian speakers want to be more specific, they can add words like:

• ova stvar = this thing
• ta stvar = that thing
• jedna stvar = one/a certain thing

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

So:

• stvar = thing
• je = is
• nekorišćena = unused

That is why the sentence means The thing is unused or The item is unused.

Because it agrees with stvar, which is feminine singular.

In Serbian, adjectives and adjective-like forms must agree with the noun in:

• gender
• number
• usually case

So you get:

• nekorišćen for masculine singular
• nekorišćena for feminine singular
• nekorišćeno for neuter singular

Since stvar is feminine, the correct form is nekorišćena.

In this sentence, it functions like an adjective meaning unused.

It comes from the verb koristiti (to use). More specifically, it is a participial form that has become adjective-like in use.

So for a learner, the easiest way to understand it is:

• koristiti = to use
• korišćen / korišćena / korišćeno = used
• nekorišćen / nekorišćena / nekorišćeno = unused

Because here ne- is part of the adjective.

In Serbian:

• with many adjectives, ne is written together
• with most verbs, ne is written separately

So:

• nekorišćena = unused as a quality/state
• nije korišćena = was not used / has not been used

This is an important difference.

Compare:

• Stvar je nekorišćena. = The item is unused.
  Focus on its condition.
• Stvar nije korišćena. = The item was not used.
  Focus on the action not happening.

In many real situations, the meanings overlap, but the grammar is different.

Stvar is in the nominative singular.

Nekorišćena is also in the nominative singular feminine, because it is used predicatively with je.

So the structure is:

• stvar = subject, nominative singular
• je = is
• nekorišćena = predicate adjective, agreeing with the subject

Yes, Serbian word order is fairly flexible, but Stvar je nekorišćena is the most neutral order.

Possible alternatives exist, but they usually sound marked or emphasize something:

• Nekorišćena je stvar. = unusual/marked, maybe poetic or contrastive
• Ta stvar je nekorišćena. = more specific: That item is unused
• Ova stvar je nekorišćena. = This item is unused

So a good default sentence is the one you have: Stvar je nekorišćena.

Yes, it is grammatical and understandable, but stvar is very general.

In real-life contexts, speakers might often choose a more specific noun, such as:

• predmet = item/object
• artikl = product/item
• roba = goods/merchandise

So depending on context, you might also hear:

• Predmet je nekorišćen.
• Ovaj artikl je nekorišćen.

Still, Stvar je nekorišćena is perfectly valid Serbian.

A rough guide is:

• ne = like neh
• ko = like koh
• riš = reesh with š = sh
• će = a soft sound, roughly like chye
• na = nah

A few useful sound notes:

• š sounds like sh in ship
• ć is a soft sound, somewhat like a softer ch
• je sounds like ye

Also, the sentence in Cyrillic is:

Ствар је некоришћена.

Yes, absolutely.

Even though stvar literally means thing, English often prefers a more natural word like:

• item
• object
• product

So depending on context, Stvar je nekorišćena could be rendered as:

• The item is unused
• The object is unused
• The thing is unused

That is a translation choice, not a grammar difference.