Bưu kiện ở bưu điện.

• bưu kiện = package / parcel
• ở = to be at / in / located at
• bưu điện = post office

So the structure is basically:

bưu kiện + ở + bưu điện
= The package is at the post office.

Because bưu is related to postal mail / post.

So:

• bưu kiện = postal package, parcel
• bưu điện = post office, postal service office

This shared element helps you see that both words belong to the same general topic: mail/postal services.

In this sentence, ở marks location. It means something like:

• is at
• is in
• is located at

So Bưu kiện ở bưu điện literally works like:

Package located-at post office

Vietnamese often uses ở where English uses is at/in.

Vietnamese does not always use a separate verb equivalent to English to be in the same way English does.

In location sentences, ở often does the job that English expresses with is at / is in.

So:

• English: The package is at the post office.
• Vietnamese: Bưu kiện ở bưu điện.

You do not need an extra word for is here.

Vietnamese commonly follows this pattern for location:

thing/person + ở + place

So:

• Tôi ở nhà. = I am at home.
• Sách ở bàn. = The book is on/at the table depending on context
• Bưu kiện ở bưu điện. = The package is at the post office.

This is a very basic and common sentence pattern.

Vietnamese does not use articles like English a / an / the.

Whether a noun is understood as a package, the package, or packages depends on context.

So bưu kiện could mean:

• a package
• the package
• sometimes packages in the right context

In this sentence, if the meaning shown to the learner is The package is at the post office, that comes from context, not from an article in Vietnamese.

Yes. Ở is broader than any single English preposition.

Depending on context, it can be translated as:

• at
• in
• on in some expressions
• located at
• live at/in when talking about residence

So Bưu kiện ở bưu điện could naturally be translated as:

• The package is at the post office
• The package is in the post office

English chooses the most natural preposition for the situation.

It can refer to the post office as a place, and in some contexts it can relate more generally to the postal system.

In Bưu kiện ở bưu điện, it clearly means the post office building/location, because the sentence is saying where the package is.

A simple tone guide:

• bưu — level tone
• kiện — heavy/falling tone
• ở — dipping-rising tone
• bưu — level tone
• điện — heavy/falling tone

A rough learner-friendly breakdown:

• bưu ≈ something like boo-uh, but compressed into one syllable
• kiện ≈ kee-en with a heavy tone
• ở ≈ a short vowel with a dipping tone
• điện ≈ dee-en with a heavy tone

A few important notes:

• đ is pronounced like English d
• tone marks matter a lot
• the vowels are not exactly like English, so listening to native audio is important

Yes. It is short, simple, and natural.

Vietnamese often allows very compact sentences when the context is clear.
So Bưu kiện ở bưu điện is a normal way to say that the package is located at the post office.

If you wanted to be more specific, you could add more information, for example:

• Bưu kiện đang ở bưu điện. = The package is currently at the post office.
• Bưu kiện của tôi ở bưu điện. = My package is at the post office.

But the original sentence is already complete.

Yes. Gói hàng is another common way to say package / parcel.

A rough difference:

• bưu kiện sounds a bit more formal or postal/logistics-related
• gói hàng is common everyday language for a package/shipment

So both can work, depending on context.
In a postal or delivery context, bưu kiện is very natural.