Muszę zapakować nieużywany towar.

Muszę is the 1st person singular form of musieć, which means to have to / must.

So:

• muszę = I have to / I must
• musisz = you have to
• musi = he/she/it has to

In this sentence, muszę tells you that the speaker is I, even though Polish does not explicitly say ja.

Polish often drops subject pronouns because the verb ending already shows who the subject is.

• Muszę already means I have to
• Ja muszę would add emphasis, like I have to or I am the one who has to

So Muszę zapakować nieużywany towar is the normal, natural version.

After muszę, Polish normally uses an infinitive:

• muszę zrobić = I have to do
• muszę iść = I have to go
• muszę zapakować = I have to pack

This works similarly to English have to + verb, except Polish uses the infinitive form directly.

This is about aspect, which is very important in Polish.

• pakować = imperfective: packing as a process, repeated action, or general activity
• zapakować = perfective: to pack something up completely, to finish packing it

With Muszę zapakować..., the idea is that the speaker needs to complete the packing.

Compare:

• Muszę pakować towar = I have to be packing the goods / I have packing to do
• Muszę zapakować towar = I have to pack the goods up completely

So zapakować is the natural choice when the goal is a finished result.

In Polish, towar is often used as a singular mass/collective-style noun meaning goods, merchandise, товар/product stock.

So even if English might use a plural word like goods, Polish can naturally use singular towar.

Compare:

• towar = goods / merchandise / product stock
• towary = goods / products (more clearly plural, often individual product types)

Both are possible in different contexts, but singular towar is very normal.

Because towar is the direct object of zapakować, it is in the accusative case.

However, towar is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular is usually the same as the nominative singular.

So:

• nominative: towar
• accusative: towar

That is why there is no visible change.

Adjectives in Polish must agree with the noun they describe in:

• gender
• number
• case

Here, towar is:

• masculine
• singular
• accusative
• inanimate

So the adjective has to match that, giving:

• nieużywany towar

For masculine inanimate singular, the accusative form of the adjective looks the same as the nominative form.

Nieużywany comes from używać = to use, with nie- added.

So literally it means something like:

• not used
• unused
• not being used

It functions here like an adjective describing towar.

You can think of it as similar to a participial adjective: the goods that are not used / unused goods.

They are related, but not always identical in nuance.

• nieużywany often suggests not used / not in use / unused as a description
• nieużyty can suggest not used up / not yet used / unused in a more result-oriented sense

In many contexts they may both translate as unused, but they do not always sound equally natural in every phrase.

In nieużywany towar, the chosen form sounds like a descriptive label for the merchandise.

Yes. Polish word order is flexible, although the original version is neutral and natural.

Neutral:

• Muszę zapakować nieużywany towar.

Possible alternatives:

• Nieużywany towar muszę zapakować.
• Muszę nieużywany towar zapakować.

These alternatives shift the emphasis:

• putting nieużywany towar first highlights the unused goods
• putting zapakować later can sound more contrastive or marked

So the original sentence is probably the best default choice unless you want special emphasis.

A rough pronunciation guide is:

MOO-sheh za-pa-KO-vach nyeh-oo-zhi-VA-nih TO-var

A more accurate IPA version is:

[ˈmuʂɛ zapaˈkɔvat͡ɕ ɲeuʐɨˈvanɨ ˈtɔvar]

A few useful pronunciation notes:

• sz sounds like sh in ship
• ż sounds like the s in measure
• w sounds like English v
• nie at the start of nieużywany is pronounced roughly nyeh
• final ę in muszę is often pronounced close to e in normal speech

So muszę is often heard roughly as MOO-sheh.