Перш ніж відправити посилку, треба написати адресу відправника.

Перш ніж means before in the sense of before doing something.

It introduces a time clause:

• Перш ніж відправити посилку = Before sending the package

Literally, перш is related to first/earlier, and ніж is a conjunction often used in comparisons or clause linking. Together, they form a fixed expression meaning before.

A very common pattern is:

• Перш ніж + infinitive
• Перш ніж + finite verb clause

For example:

• Перш ніж піти, вимкни світло. = Before leaving, turn off the light.
• Перш ніж ти підеш, поговорімо. = Before you leave, let’s talk.

Відправити is the perfective infinitive, while відправляти is the imperfective infinitive.

In this sentence, the perfective form is used because it refers to a completed action:

• відправити посилку = to send the package as one whole completed event

This fits well with before:

• Before sending the package, ... The idea is that the package has not yet been sent, but the action is viewed as a single completed step.

Compare:

• відправити = to send, to dispatch once, successfully complete the sending
• відправляти = to be sending, to send repeatedly, or to focus on the process

Because посилку is in the accusative case.

The verb відправити takes a direct object, and in Ukrainian the direct object often goes into the accusative:

• nominative: посилка = package
• accusative: посилку = package, as the thing being sent

So:

• відправити що? → посилку

This is very common with feminine nouns ending in -а:

• книга → книгу
• машина → машину
• адреса → адресу

Треба means it is necessary, one must, or simply need to.

Ukrainian often uses impersonal constructions where English would use a subject such as you, we, or one.

So:

• треба написати адресу відправника = it is necessary to write the sender’s address
• in natural English: you need to write the sender’s address

There is no explicit subject because Ukrainian does not need one here. The sentence is about a general requirement, not about a specific person.

You may also see:

• потрібно = necessary / need to
• слід = should / ought to

Again, this is about aspect.

• написати = perfective, to write down / complete the writing
• писати = imperfective, to write / be writing / write in general

Here the sentence means that the address must be written as a completed action before the package is sent. That is why написати is natural.

Compare:

• Треба написати адресу. = You need to write the address down.
• Я люблю писати листи. = I like writing letters.

For the same reason as посилку: it is the direct object of the verb написати, so it goes into the accusative case.

• nominative: адреса
• accusative: адресу

Question test:

• написати що? → адресу

So:

• написати адресу відправника = to write the sender’s address

Відправника is in the genitive case.

It depends on адресу and means of the sender:

• адресу відправника = the sender’s address
• literally: the address of the sender

This is a very common Ukrainian pattern:

• номер телефону = phone number
• двері будинку = the house’s door / the door of the house
• ім’я вчителя = the teacher’s name

So:

• nominative: відправник = sender
• genitive: відправника = of the sender

Usually Ukrainian expresses this idea with a noun in the genitive, not with an apostrophe-like possessive structure as in English.

So the normal way is:

• адреса відправника = sender’s address
• адреса одержувача = recipient’s address

This is one of the most important differences from English. Where English often uses X’s Y, Ukrainian very often uses:

• Y + genitive of X

Because Перш ніж відправити посилку is an introductory subordinate clause, and it is separated from the main clause by a comma.

Structure:

• subordinate clause: Перш ніж відправити посилку
• main clause: треба написати адресу відправника

So the comma works like English:

• Before sending the package, you need to write the sender’s address.

In Ukrainian, commas before or after subordinate clauses are very important and are used more consistently than in English.

The word order is fairly natural, but Ukrainian word order is more flexible than English.

The given sentence is neutral and clear:

• Перш ніж відправити посилку, треба написати адресу відправника.

You could also say:

• Треба написати адресу відправника, перш ніж відправити посилку.

Both are correct. The difference is mainly in emphasis:

• starting with Перш ніж... highlights the time condition first
• starting with Треба... highlights the obligation first

Yes, надіслати is also possible, and in many contexts it is very natural.

Compare:

• відправити посилку
• надіслати посилку

Both can mean to send a package. In everyday usage, they are often close in meaning.
Very roughly:

• відправити can feel like dispatch/send off
• надіслати often corresponds closely to send

So you could also say:

• Перш ніж надіслати посилку, треба написати адресу відправника.

That would still be correct and natural.

Yes. Grammatically, it specifically means the sender’s address.

• відправник = sender
• одержувач = recipient / addressee

So:

• адреса відправника = sender’s address
• адреса одержувача = recipient’s address

If both were meant, Ukrainian would normally say so explicitly.

A more conversational version might be:

• Перед тим як відправити посилку, треба написати адресу відправника.
• Перед відправленням посилки треба написати адресу відправника.

The original sentence is completely normal, but перед тим як is also very common in speech and may feel a bit easier for learners because it maps closely to before doing / before you do.

Still, Перш ніж... is standard, natural, and worth learning.