Lan dùng cây lau nhà để lau sàn nhà.

The two instances of lau are doing different jobs:

• In cây lau nhà, lau is part of the noun phrase meaning mop.

  • cây = a classifier/noun often used for stick-like objects
  • lau nhà = clean the floor/house by wiping
  • So cây lau nhà literally suggests the stick/tool for wiping the floor, which is a mop.

• In để lau sàn nhà, lau is the main verb to wipe / mop / clean by wiping.

So even though the same word appears twice, one is inside the name of the tool, and the other is the action itself.

Dùng means to use.

So:

• Lan dùng cây lau nhà... = Lan uses a mop...

This is a very common verb in Vietnamese for use:

• dùng điện thoại = use a phone
• dùng đũa = use chopsticks

In this sentence, dùng introduces the instrument that Lan uses to do the action.

Here, để means something like in order to.

So:

• dùng cây lau nhà để lau sàn nhà = use a mop in order to clean the floor

A very literal breakdown is:

• Lan = Lan
• dùng = uses
• cây lau nhà = a mop
• để = in order to
• lau sàn nhà = wipe/mop the floor

In natural English, we usually would not say uses a mop in order to mop the floor, because it sounds repetitive. But in Vietnamese, this structure is perfectly normal.

Usually, để is helpful here because it clearly links the tool and the purpose.

• Lan dùng cây lau nhà để lau sàn nhà.
  = natural and clear

If you remove để, the sentence can sound less smooth or less clear:

• Lan dùng cây lau nhà lau sàn nhà.

A Vietnamese speaker may still understand it, but để makes the structure easier and more standard: use X to do Y.

No. Although cây can mean tree, it also has another common use: it can refer to a long, stick-like object, or function as a classifier for such objects.

In cây lau nhà, cây is part of the noun for the object:

• cây lau nhà = mop

You will see cây in many object names:

• cây bút = pen
• cây dao = knife (in some contexts/dialects, though con dao is more common)
• cây chổi = broom

So here cây does not mean tree. It helps form the noun referring to the cleaning tool.

Because it is part of two different expressions:

• cây lau nhà = mop
• sàn nhà = floor of the house/building

In cây lau nhà, nhà is part of the fixed expression for the cleaning tool. In sàn nhà, nhà specifies that it is the house floor / indoor floor, not just any surface.

So the repeated nhà is not a mistake. It belongs to two separate phrases.

They are related, but not exactly the same.

• lau nhà often means to mop/clean the floor, and in everyday speech it can refer more generally to cleaning the house floor area.
• lau sàn nhà is more specific: to wipe/mop the floor surface.

So:

• cây lau nhà is the standard word for mop
• lau sàn nhà describes the action more explicitly: mop the floor

Vietnamese often allows this kind of overlap between a common object name and a more specific action phrase.

No. There are a few possibilities, depending on context.

• sàn nhà = floor surface, often a bit more explicit
• nền nhà = floor, especially the ground/floor inside a house
• Sometimes people simply say nhà in context when talking about mopping the floor

For example:

• Lan lau sàn nhà.
• Lan lau nền nhà.

Both can work, though the most natural choice may vary by region and situation.

Vietnamese usually does not require articles like a, an, or the.

So:

• cây lau nhà can mean a mop or the mop
• sàn nhà can mean the floor or a floor, depending on context

You figure it out from the situation rather than from an article.

That is very normal in Vietnamese. English speakers often expect an article, but Vietnamese usually leaves it out unless there is some other determiner.

The structure is:

• Lan = subject
• dùng = verb
• cây lau nhà = object/instrument being used
• để lau sàn nhà = purpose phrase

So the pattern is roughly:

Subject + dùng + tool + để + action

A literal gloss would be:

Lan uses mop in-order-to wipe floor

This is a very common Vietnamese pattern for saying someone uses something to do something.

Yes, that is also natural.

• Lan dùng cây lau nhà để lau sàn nhà. = Lan uses a mop to mop the floor.
• Lan lau sàn nhà bằng cây lau nhà. = Lan mops the floor with a mop.

The difference is mostly in focus:

• dùng ... để ... emphasizes using a tool for a purpose
• bằng emphasizes with / by means of

Both are correct and useful.

Not exactly. Lan is a proper name, so it simply names the person.

Vietnamese often uses names where English might use a pronoun, especially when the person has already been introduced or when speaking naturally in context.

So in another sentence, Vietnamese might continue using Lan instead of switching to she, depending on style and context.

It is best to learn it as a chunk: cây lau nhà = mop.

You can still benefit from understanding the parts:

• cây = stick-like object / classifier
• lau = wipe
• nhà = house/home

But if you try to build the meaning fresh every time, it may feel awkward. For learners, the most practical approach is:

• memorize cây lau nhà = mop
• memorize lau sàn nhà = mop the floor

Then later, the internal logic will feel more natural.