Sáng nay, tôi phải đi cầu thang vì thang máy bị hỏng.

Sáng nay means this morning.

Vietnamese often puts time expressions near the beginning of the sentence to set the time frame first. So Sáng nay, tôi phải... is a very natural way to say This morning, I had to...

Also, nay in this expression means something like today/this, so sáng nay is literally morning today.

Vietnamese usually does not mark tense the way English does.

In this sentence:

• Sáng nay tells you the action happened earlier today, so English translates it in the past: had to
• thang máy bị hỏng means the elevator was broken or the elevator had broken down

There is also no separate word for was here. Vietnamese often describes states directly, without a verb like to be in English. So:

• thang máy bị hỏng = the elevator was broken
• not something like thang máy là bị hỏng

Phải means must, have to, or need to, depending on context.

In tôi phải đi cầu thang, it shows necessity:

• tôi phải... = I have to... / I must...

Because the sentence is set in the past by Sáng nay, English naturally becomes I had to take the stairs.

So phải itself does not mean specifically present or past; the time comes from context.

Yes, đi basically means to go, but it is also used more broadly for movement or using a route/method of travel.

So đi cầu thang means something like:

• go by the stairs
• take the stairs

It does not mean you are literally saying go staircase word-for-word in English. It is a natural Vietnamese way to talk about using the stairs.

If you want to emphasize direction, Vietnamese often uses:

• lên cầu thang = go up the stairs
• xuống cầu thang = go down the stairs

They are two different compounds:

• cầu thang = stairs / staircase
• thang máy = elevator / lift

Even though both contain thang, you should learn them as whole words:

• cầu thang is not understood as just bridge + ladder in normal use
• thang máy is the normal word for an elevator

So in this sentence:

• đi cầu thang = use the stairs
• thang máy bị hỏng = the elevator was broken

It is understandable and can sound natural, but many speakers would also say:

• đi thang bộ
• đi cầu thang bộ

These forms make the contrast with the elevator especially clear.

So the original sentence is fine, but depending on the speaker or region, you may also hear:

• Sáng nay, tôi phải đi thang bộ vì thang máy bị hỏng.

That is often a very natural everyday way to say I had to take the stairs because the elevator was broken.

Vì means because.

In the sentence:

• vì thang máy bị hỏng = because the elevator was broken

Yes, the reason can come first. You could also say:

• Vì thang máy bị hỏng, sáng nay tôi phải đi cầu thang.

That means the same thing. The difference is mainly in emphasis and style:

• main clause first + vì clause after it = very common in speech
• vì clause first = also correct, sometimes a bit more formal or more clearly structured

Hỏng means broken, damaged, or out of order.

Bị is often used when something happens to the subject, especially something negative or unwanted. So:

• thang máy hỏng = the elevator is broken
• thang máy bị hỏng = the elevator got broken / was broken, with a stronger sense that this is an unfortunate situation

In everyday speech, both are common. Adding bị often makes the sentence sound a bit more complete or emphasizes the bad result.

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

So bare nouns are very common:

• cầu thang = stairs / the stairs
• thang máy = elevator / the elevator

Context tells you whether the noun is specific. In this sentence, it is obvious which elevator is meant, so thang máy is enough.

If Vietnamese wants to be more specific, it can add words such as:

• cái thang máy này = this elevator
• cái thang máy đó = that elevator

But in the original sentence, no extra marker is needed.

The comma is common and helpful, but not always absolutely necessary.

Both of these are normal:

• Sáng nay, tôi phải đi cầu thang vì thang máy bị hỏng.
• Sáng nay tôi phải đi cầu thang vì thang máy bị hỏng.

The comma simply marks Sáng nay as a sentence-opening time phrase, a little like a pause in speech.

Sometimes yes, if the context already makes it clear who is speaking about themselves.

For example, in conversation, a speaker might say:

• Sáng nay phải đi cầu thang vì thang máy bị hỏng.

That can still be understood as This morning, I had to take the stairs because the elevator was broken.

But including tôi is clearer and very normal, especially for learners and in standalone sentences.