Learn Hardcore Vietnamese: Buổi tối Lan thích tắm vì cô ấy làm việc ở công ty. - In the evening, Lan likes to shower because she works at a company.

Together, buổi tối means the evening / evenings / in the evening, depending on context. Vietnamese doesn’t need a separate preposition like in here:

Buổi tối Lan thích tắm → In the evening, Lan likes to bathe.

You could also say vào buổi tối (literally "enter/at the evening") for extra clarity, but in many everyday sentences buổi tối at the start is enough to express "in the evening".

Why is there no word like to in Lan thích tắm? In English we say "Lan likes to bathe."

Vietnamese does not use a particle like to before the second verb.

The structure is simply:

[Subject] + [Verb of liking/wanting] + [Verb]

So:

Lan thích tắm = Lan likes (to) bathe.
Tôi muốn ăn = I want (to) eat.
Anh ấy thích đọc sách = He likes (to) read books.

The second verb (tắm, ăn, đọc) directly follows the first verb without anything in between.

What is the function of vì in this sentence, and can it come at the beginning like because?

Vì means because and introduces a reason clause.

In the given sentence:

Lan thích tắm – Lan likes to bathe
vì cô ấy làm việc ở công ty – because she works at a company

Word order can be flexible:

Main clause first (as in the example):
- Buổi tối Lan thích tắm vì cô ấy làm việc ở công ty.
  → In the evening, Lan likes to bathe because she works at a company.
Reason first (more like English "Because… , …"):
- Vì cô ấy làm việc ở công ty, buổi tối Lan thích tắm.
  → Because she works at a company, in the evening Lan likes to bathe.

Both are natural. Vietnamese speakers often put the reason clause either before or after, depending on emphasis and style.

Why do we say cô ấy instead of just repeating Lan, and what does cô ấy literally mean?

Cô ấy is a third‑person feminine pronoun, roughly she / her.

cô – literally "young woman / Ms. / aunt (on father’s side)" but often used in pronouns for a young/younger adult woman
ấy – "that" (used here to form a third‑person pronoun)

Together, cô ấy = she (that young woman).

We could repeat the name:

... vì Lan làm việc ở công ty.

But using cô ấy is more natural here once Lan has already been introduced. Vietnamese commonly switches between a person’s name and a pronoun, a bit like English switches between Lan and she.

Could we drop the subject in the vì clause and just say vì làm việc ở công ty?

Yes, that is possible and often sounds quite natural in context:

Buổi tối Lan thích tắm vì làm việc ở công ty.

Here, the subject cô ấy / Lan is understood from the previous clause.

However, including cô ấy:

vì cô ấy làm việc ở công ty

is clearer (especially in written language or longer sentences) and is the more "complete" form. Both versions are grammatically acceptable.

Why is there no tense marker like does or works? How do we know it’s present time?

Vietnamese verbs do not change form for tense. Time is usually shown by:

Context/time words (like buổi tối)
Optional particles (such as đã, đang, sẽ)

In this sentence:

Buổi tối – "in the evening"
Lan thích tắm – Lan like(s) to bathe
cô ấy làm việc ở công ty – she work(s) at a company

Because we are talking about a regular habit (evenings, work), the natural English translation uses the present simple:

In the evening, Lan likes to bathe because she works at a company.

If you wanted to make past or future explicit, you’d add particles:

Hôm qua buổi tối Lan thích tắm vì cô ấy đã làm việc ở công ty.
→ Last night Lan liked to bathe because she had worked at the company.
Ngày mai buổi tối Lan sẽ tắm vì cô ấy sẽ làm việc ở công ty.
→ Tomorrow evening Lan will bathe because she will work at the company.

What does ở add in ở công ty? Can we just say làm việc công ty?

Ở is a preposition roughly meaning at / in / at the place of.

làm việc ở công ty – work at a company

Without ở, làm việc công ty is not natural; it sounds like a noun phrase ("company work") rather than "work at a company."

So:

làm việc ở nhà – work at home
học ở trường – study at school
làm việc ở công ty – work at a company

Why is there no word for a or the before công ty? Should it be một công ty?

Vietnamese does not have articles like a / an / the. Whether công ty means a company, the company, or (her) company depends on context.

làm việc ở công ty – work at a company / at the company

If you specifically want to say a company (non‑specific), you can say:

làm việc ở một công ty – work at a company

If you want to refer to a particular, known company, you might specify:

làm việc ở công ty đó – work at that company
làm việc ở công ty ABC – work at ABC Company

In everyday speech, ở công ty is often understood as "at (her) company / at the office."

Does tắm mean "to bathe" or "to shower"? Is it only for baths?

Tắm is a general verb meaning to wash the body, and in modern usage it usually covers both:

to take a bath
to take a shower

Whether it’s a tub or a shower is usually not important, and Vietnamese speakers still just say tắm:

Buổi tối Lan thích tắm.
→ In the evening, Lan likes to shower / take a bath.

If you need to be specific, you can add more detail:

tắm vòi sen – shower
tắm bồn – take a bath (in a tub)

Is the word order Buổi tối Lan thích tắm fixed, or can we move the time phrase?

Vietnamese word order is fairly flexible with time expressions.

All of these are grammatical:

Buổi tối Lan thích tắm.
→ In the evening, Lan likes to bathe. (time first)
Lan buổi tối thích tắm.
→ Lan, in the evening, likes to bathe. (less common, more marked)
Lan thích tắm buổi tối.
→ Lan likes to bathe in the evening. (common and natural)

Placing buổi tối at the beginning (as in the original sentence) is very common and sounds slightly more formal or descriptive. Putting it at the end is also very natural in casual speech.