Nu expedia coletul fără să atașezi eticheta.

Because this is a negative singular command.

In Romanian, the negative imperative for tu is usually formed with:

nu + infinitive

So:

• a expedia = to ship / to send
• Nu expedia! = Don’t ship!

By contrast, expediezi is the normal present tense form meaning you ship / you are shipping, not the usual command form here.

A very useful comparison is:

• Expediază coletul! = Ship the package!
• Nu expedia coletul! = Don’t ship the package!

So the positive and negative tu commands often look different.

The ending -ul is the definite article attached to the noun.

Romanian usually puts the at the end of the noun instead of as a separate word.

• colet = package / parcel
• coletul = the package / the parcel

So:

• expedia coletul = ship the package
• not just ship a package

This is one of the most important basic features of Romanian grammar.

Romanian often uses fără să + verb where English uses without + -ing.

So:

• fără să atașezi eticheta = without attaching the label
• literally: without that you attach the label

This is a very common Romanian structure.

You may also sometimes see the more formal pattern:

• fără a atașa eticheta

That also means without attaching the label, but fără să atașezi is very natural and common in everyday language.

Să is the marker that usually introduces the subjunctive in Romanian.

In this sentence:

• fără să atașezi = without attaching

The verb after să is in the subjunctive pattern. For many verbs, the form after să looks the same as the present tense, but să still signals the construction.

Examples:

• să pleci = that you leave / for you to leave
• să faci = that you do
• să atașezi = that you attach

Here, you do not need to translate să word-for-word. It is mainly a grammar marker.

Atașezi is the 2nd person singular form, matching an understood you.

The whole sentence is addressed to one person:

• Nu expedia ... = Don’t ship ...
• fără să atașezi ... = without attaching ...

So the same implied you continues through the sentence.

The base verb is:

• a atașa = to attach

Relevant forms:

• atașezi = you attach
• să atașezi = that you attach / for you to attach

Because Romanian often leaves out subject pronouns when they are already clear from the verb form.

In commands, this is especially normal.

So:

• Nu expedia coletul... already clearly means Don’t you ship the package...
• atașezi also tells us it is addressed to you singular

You could add tu for emphasis:

• Tu nu expedia coletul fără să atașezi eticheta.

But that would usually sound more emphatic, contrastive, or corrective. The version without tu is the normal one.

Because eticheta means the label.

Just like coletul, it has the Romanian definite article attached to the noun:

• etichetă = label
• eticheta = the label

So the sentence refers to a specific label that should go on the package.

Note that the noun is feminine, so the definite form looks different from coletul:

• masculine/neuter singular often: -ul
• feminine singular often: -a

Colet is a neuter noun.

In Romanian, neuter nouns behave:

• like masculine in the singular
• like feminine in the plural

So in the singular you get:

• un colet
• coletul

That is why it looks masculine here.

If you made it plural, you would see the neuter behavior more clearly:

• colete = packages
• coletele = the packages

The positive singular command is different:

• Expediază coletul! = Ship the package!

So compare:

• Expediază! = positive command
• Nu expedia! = negative command

This difference is very common in Romanian tu imperatives:

• Spune! / Nu spune!
• Pleacă! / Nu pleca!
• Trimite! / Nu trimite!

In your sentence, the positive version would be:

• Expediază coletul după ce atașezi eticheta.
  or simply
• Atașează eticheta și expediază coletul.

Yes. A trimite is another common verb meaning to send.

So:

• Nu trimite coletul fără să atașezi eticheta.

is also grammatical and natural.

The difference is mostly one of nuance and register:

• a expedia often sounds a bit more specific to shipping, dispatching, or sending something formally/logistically
• a trimite is broader and very common in everyday language

In many contexts, both are fine.

The given word order is the most neutral and natural:

• Nu expedia coletul fără să atașezi eticheta.

Romanian word order is fairly flexible, but changing it can shift the emphasis.

For example:

• Fără să atașezi eticheta, nu expedia coletul.

This is also correct, but it emphasizes the without attaching the label part first.

So the original order is probably the best choice for a straightforward instruction.

A rough pronunciation guide is:

Noo ex-pe-dee-A ko-LE-tul fə-RƏ sə a-ta-SHEZ ee e-ti-KHE-ta

A few useful notes:

• nu sounds like noo
• expedia has the stress near the end: ex-pe-di-A
• coletul is roughly ko-LE-tul
• fără has the Romanian vowel ă, a short neutral sound, something like the a in sofa
• să also contains ă
• atașezi has ș, pronounced like sh
• eticheta is roughly e-ti-KHE-ta, with ch pronounced like k before e

If you want a more learner-friendly rhythm, you can chunk it like this:

Nu expedia / coletul / fără să atașezi / eticheta.