Nieużywany towar jest w oryginalnym opakowaniu.

Because here it functions as an adjective meaning unused. In Polish, nie- is usually written together with adjectives, so nieużywany towar is the normal spelling in this kind of description.

You may sometimes see separate spelling in more verbal or contrastive contexts, but for a product description, nieużywany is the standard form.

It is an adjective-like form meaning unused or not used.

It comes from the verb używać (to use), but in this sentence it behaves like an adjective:

• it describes the noun towar
• it changes its ending to match the noun in gender, number, and case

So nieużywany towar is literally unused товар/item/goods.

Because nieużywany has to agree with towar.

Here, towar is:

• masculine
• singular
• nominative

So the adjective also takes the masculine singular nominative form:

• nieużywany towar

If the noun changed, the adjective would change too:

• nieużywana rzecz
• nieużywane urządzenie
• nieużywane towary

Because towar is the subject of the sentence, and subjects normally appear in the nominative case.

The structure is:

• Nieużywany towar = the subject
• jest = is
• w oryginalnym opakowaniu = location/state

So nominative towar is the expected form.

Here towar is singular.

In business or sales language, towar means something like:

• goods
• merchandise
• item
• product

Even though English often uses goods as a plural word, Polish towar can be singular. In this sentence it refers to one item or one unit of merchandise.

In a normal full sentence, jest is natural and expected.

Polish often omits to be in:

• headlines
• notes
• labels
• very compressed speech

But in a standard sentence like this, jest makes it complete:

• Nieużywany towar jest w oryginalnym opakowaniu.

A shorter listing style might drop it, but that sounds more like a sales note than a full sentence:

• Nieużywany towar w oryginalnym opakowaniu

After w meaning in, Polish normally uses the locative case when talking about location.

So:

• w = in
• opakowanie = packaging
• locative singular of opakowanie = opakowaniu

The adjective must agree with the noun, so:

• oryginalne opakowanie → nominative
• w oryginalnym opakowaniu → locative

That is why both words change:

• oryginalne → oryginalnym
• opakowanie → opakowaniu

Because the adjective has to match opakowaniu.

Since opakowaniu is:

• singular
• neuter
• locative

the adjective must also be:

• singular
• neuter
• locative

So you get:

• w oryginalnym opakowaniu

This is a very common Polish pattern: adjectives agree with the nouns they describe.

Polish often leaves out possessive words when the meaning is obvious from context.

So w oryginalnym opakowaniu naturally means:

• in original packaging
• in the original packaging
• often, in context, in its original packaging

If you wanted to make the possession explicit, you could say:

• w swoim oryginalnym opakowaniu

But that is more explicit than necessary in many contexts. The version without swoim is very normal.

Because Polish has no articles.

English distinguishes:

• a product
• the product

Polish usually does not. Context tells you whether something is definite or indefinite.

So Nieużywany towar jest w oryginalnym opakowaniu can be understood as:

• The unused item is in the original packaging or
• An unused item is in original packaging

depending on context.

Yes, Polish word order is more flexible than English, although not completely free.

This version is neutral and natural:

• Nieużywany towar jest w oryginalnym opakowaniu.

Other orders are possible for emphasis, for example:

• Towar jest nieużywany i w oryginalnym opakowaniu.

But the original sounds like a straightforward product description. English speakers should usually learn the neutral order first.

A rough English-style guide is:

• Nieużywany → nyeh-oo-zhih-VA-nih
• towar → TO-var
• jest → yest
• w → v
• oryginalnym → o-ri-gi-NAHL-nim
• opakowaniu → o-pa-ko-VA-nyoo

A few useful pronunciation points:

• ż sounds like the s in measure
• w sounds like English v
• stress is usually on the second-to-last syllable

So the whole sentence is roughly: nyeh-oo-zhih-VA-nih TO-var yest v o-ri-gi-NAHL-nim o-pa-ko-VA-nyoo