Tôi phải đóng cửa trước khi đi ngủ.

Phải shows necessity or obligation. In this sentence, it means have to / must.

So Tôi phải đóng cửa... means I have to close the door...

A useful comparison:

• phải = must / have to
• muốn = want to
• cần = need

So:

• Tôi phải đóng cửa. = I have to close the door.
• Tôi muốn đóng cửa. = I want to close the door.

Vietnamese word order here is:

subject + modal verb + main verb + object

So:

• Tôi = I
• phải = must / have to
• đóng = close
• cửa = door

That gives:

Tôi phải đóng cửa = I have to close the door

The modal phải comes before the main verb đóng, just like must comes before close in English.

Yes, đóng cửa is a very common verb phrase meaning to close the door.

Breakdown:

• đóng = close, shut
• cửa = door

It can be used literally, as in this sentence, but đóng cửa can also sometimes mean to shut a business/store depending on context.

Examples:

• Đóng cửa lại. = Close the door.
• Cửa hàng đóng cửa lúc 9 giờ. = The shop closes at 9 o’clock.

So in your sentence, it simply means close the door.

Vietnamese usually does not use articles like a, an, or the the way English does.

So cửa can mean:

• a door
• the door

The exact meaning depends on context.

In this sentence, English naturally says the door, but Vietnamese just says cửa.

This is very normal in Vietnamese.

trước khi means before when it introduces an action or clause.

Breakdown:

• trước = before
• khi = when

Together, trước khi works like before in before doing something / before someone does something.

So:

• trước khi đi ngủ = before going to sleep / before I go to sleep

Why not just trước?

Because trước khi is the natural pattern before a verb clause.

Compare:

• trước khi ăn = before eating
• trước khi học = before studying
• trước khi đi ngủ = before going to sleep

Vietnamese often omits the subject in the second clause if it is already clear from context.

So:

• Tôi phải đóng cửa trước khi đi ngủ.

is understood as:

• Tôi phải đóng cửa trước khi tôi đi ngủ.

Both make sense, but repeating tôi is often unnecessary.

This is very common in Vietnamese and sounds natural.

Literally, đi ngủ is something like go sleep:

• đi = go
• ngủ = sleep

But as a phrase, it means:

• go to sleep
• go to bed
  depending on context

So in this sentence, trước khi đi ngủ means before going to sleep / before going to bed.

Vietnamese often uses đi + verb in expressions of beginning or going to do something.

Yes, you often can.

• trước khi ngủ = before sleeping
• trước khi đi ngủ = before going to sleep / before going to bed

The difference is small:

• ngủ focuses on sleeping
• đi ngủ focuses a bit more on the act of going to bed / going to sleep

In everyday speech, both can work, and both are natural in many contexts.

Sometimes, yes.

If the subject is obvious from context, Vietnamese often drops pronouns. So in conversation, someone might simply say:

• Phải đóng cửa trước khi đi ngủ.

This can mean (I/you/we) have to close the door before going to sleep, depending on context.

But with no context, tôi makes the sentence clearer: I have to close the door before going to sleep.

A common way is:

• Tôi cần đóng cửa trước khi đi ngủ.

But there is a nuance:

• phải = stronger, more like must / have to
• cần = need to, often a bit softer

So:

• Tôi phải đóng cửa... = I really have to / must close the door
• Tôi cần đóng cửa... = I need to close the door

In many situations, phải is the more natural choice for obligation.

A rough pronunciation guide is:

Tôi phải đóng cửa trước khi đi ngủ.
≈ toy feye dohng koo-uh tru-uk khee dee ngoo

This is only approximate, because Vietnamese tones are very important.

A few notes:

• tôi has a level-ish tone
• phải has a dipping/rising tone
• đóng has a rising tone
• cửa has a broken/dipping tone in Northern pronunciation
• ngủ also has a broken/dipping tone

If you are learning pronunciation, it is best to listen to native audio and imitate the full rhythm of the sentence, not just the individual words.

Not always. Cửa can mean several related things depending on context, such as:

• door
• gate
• entrance
• sometimes part of expressions involving opening/closing

In đóng cửa, it most naturally means door or doorway/gate, depending on the situation.

So here, the intended meaning is simply close the door.