Hôm nay tôi quên mang ô, nên ví của tôi bị ướt khi đi từ trạm xe buýt về nhà.

Yes, ô has several meanings in Vietnamese depending on context. In this sentence, mang ô clearly means bring an umbrella.

Common meanings of ô include:

• umbrella / parasol
• a square / box / cell, as in a table or grid
• part of some compound words

Here, because it comes after mang (to carry / bring), the meaning umbrella is the natural one.

Quên mang ô means forgot to bring an umbrella.

• quên = to forget
• mang = to carry / bring on your person

So quên mang ô is literally forgot to carry/bring an umbrella.

A native English speaker may expect something like forgot the umbrella, but Vietnamese often expresses this idea as forgot to bring the item.

Also, mang and đem can both relate to bringing something, but:

• mang often emphasizes carrying something with you
• đem often emphasizes taking/bringing something somewhere

In this sentence, mang ô sounds very natural.

Nên here means so or therefore.

The structure is:

• Hôm nay tôi quên mang ô, nên...
• Today I forgot to bring an umbrella, so...

It connects cause and result:

• cause: I forgot to bring an umbrella
• result: my wallet got wet

So nên is a very common way to link two clauses when the second is the consequence of the first.

Ví của tôi means my wallet.

• ví = wallet
• của tôi = of me / my

In Vietnamese, possession is often shown with của:

• nhà của tôi = my house
• sách của tôi = my book
• ví của tôi = my wallet

However, in everyday speech, Vietnamese often omits của when the meaning is clear:

• ví tôi can also be understood as my wallet

That said:

• ví của tôi is very clear and grammatical
• ví tôi may sound a bit more natural in casual speech in some contexts

Both are possible, but ví của tôi is especially easy for learners to understand.

Bị ướt means got wet.

• ướt = wet
• bị often marks something negative, unwanted, or unfortunate happening to the subject

So:

• ví của tôi bị ướt = my wallet got wet / my wallet was made wet in an unfortunate way

This is a very common Vietnamese pattern:

• bị mất = got lost
• bị hỏng = got broken
• bị đau = got hurt / is suffering pain
• bị ướt = got wet

Using bị adds the sense that this was not intentional and was unpleasant.

Yes, you could, but the nuance is slightly different.

• Ví của tôi ướt = my wallet is wet
• Ví của tôi bị ướt = my wallet got wet / ended up wet, with a sense of unfortunate result

So:

• ướt alone describes the state
• bị ướt highlights the event or misfortune

In this sentence, bị ướt fits well because the wetness happened as a result of forgetting the umbrella.

The subject is understood from context: it is tôi (I).

Vietnamese often omits a repeated subject when it is obvious.

So:

• khi đi từ trạm xe buýt về nhà means
• when walking from the bus stop home or more naturally in English
• when I was walking home from the bus stop

If you wanted to make it completely explicit, you could say:

• khi tôi đi từ trạm xe buýt về nhà

But omitting tôi here is very normal.

This shows movement from one place to another:

• từ = from
• trạm xe buýt = bus stop
• về nhà = go home / return home

So:

• đi từ trạm xe buýt về nhà = go from the bus stop home

A useful pattern is:

• đi từ A đến B = go from A to B
• đi từ A về nhà = go from A home

Vietnamese uses về especially when going back to a familiar place, especially home.

So về nhà is more natural than đến nhà here.

Trạm xe buýt means bus stop.

Breakdown:

• trạm = station / stop
• xe buýt = bus

This is a standard and common term.

You may also hear:

• bến xe buýt

Depending on region and context, both can appear, but trạm xe buýt is very clear and natural for bus stop.

Yes, Vietnamese often puts time expressions near the beginning of the sentence.

• Hôm nay tôi quên mang ô... = Today I forgot to bring an umbrella...

This is very common because Vietnamese frequently sets the time first, then gives the event.

You can move time expressions in some cases, but sentence-initial position is especially natural:

• Hôm nay tôi...
• Sáng nay tôi...
• Hôm qua tôi...

So the word order here is completely normal.

This is a great question because they are easy to confuse.

• ví = wallet
• vì = because

The tones are different:

• ví has the sắc tone
• vì has the huyền tone

In your sentence:

• ví của tôi = my wallet

If it were vì, that would not fit here.

This is a good example of how important tone marks are in Vietnamese: a small written difference can create a completely different word.

Yes, it is natural and understandable. A native speaker might also say it in slightly different ways, for example:

• Hôm nay tôi quên mang ô, nên ví tôi bị ướt lúc đi từ trạm xe buýt về nhà.
• Hôm nay tôi quên mang ô, nên lúc đi từ trạm xe buýt về nhà, ví tôi bị ướt.

These versions mainly differ in word order or in whether của is included.

The original sentence is perfectly good Vietnamese. It is also a useful learner sentence because the grammar is clear:

• time expression
• cause/result with nên
• possession with của
• negative-result marker bị
• omitted subject in a subordinate clause

Yes. In this sentence, khi and lúc are both possible.

• khi đi từ trạm xe buýt về nhà
• lúc đi từ trạm xe buýt về nhà

Both mean when going/walking home from the bus stop.

Very roughly:

• khi can feel a bit more neutral or formal
• lúc can feel a bit more conversational in some contexts

But in everyday Vietnamese, both are common and natural here.