qǐng nǐ yòng máojīn cā yí xià shǒu.

A helpful way to see it is:

请你 + 用毛巾 + 擦一下 + 手

That breaks down as:

• 请你 = please / please would you...
• 用毛巾 = use a towel / with a towel
• 擦一下 = wipe for a moment / give a quick wipe
• 手 = hands

So the sentence follows a very common Mandarin pattern:

[polite request] + [method/instrument] + [verb] + [object]

In more natural English structure, this is something like:

• Please use a towel to wipe your hands.
• Please wipe your hands with a towel.

Mandarin often puts the tool or means before the main verb, using 用.

Yes, literally it is please + you, but in natural English we would not translate it word-for-word.

Here, 请 is being used to make a polite request. So 请你... means something like:

• Please...
• Please would you...
• Would you please...

So:

• 请你用毛巾擦一下手。
  = Please wipe your hands with a towel.

A few useful notes:

• 请 can also mean to invite in other contexts.
• In requests, 请你... sounds polite but direct.
• Very often, 你 can be omitted if the listener is obvious:
  • 请用毛巾擦一下手。

用 means to use.

In this sentence, it introduces the instrument or tool used to do the action:

• 用毛巾 = using a towel / with a towel

So Mandarin says:

• use towel wipe hands

where English usually says:

• wipe your hands with a towel

This is a very common pattern:

• 用筷子吃饭 = eat with chopsticks
• 用笔写字 = write with a pen
• 用手机拍照 = take pictures with a phone

So 用毛巾擦手 is completely natural Mandarin for wipe your hands with a towel.

擦 means to wipe, to rub, or sometimes to clean by wiping.

The 一下 is very common after verbs. It often makes the action sound:

• lighter
• shorter
• less abrupt
• more casual or polite

So:

• 擦手 = wipe your hands
• 擦一下手 = wipe your hands a bit / give your hands a quick wipe

In requests and commands, 一下 often softens the tone. It does not always literally mean one time in a strict sense. It often just makes the sentence sound more natural and less harsh.

Compare:

• 擦手。 = Wipe your hands.
  (more blunt)
• 擦一下手。 = Wipe your hands for a moment / just wipe your hands.
  (softer, more natural)

This is because of tone sandhi.

Normally, 一 is pronounced yī. But its pronunciation changes depending on the tone of the following syllable.

Before a fourth-tone syllable, 一 changes to yí.

Here:

• 下 is xià (fourth tone)
• so 一下 is pronounced yíxià

This change is only in pronunciation; the character is still 一.

A quick summary:

• 一 by itself: usually yī
• before a 4th tone: yí
• before other tones: often yì

So:

• 一下 = yíxià
• 一点 = yìdiǎn

In Mandarin, body parts often appear without possessives like 你的 when the owner is obvious from context.

So:

• 擦一下手 literally looks like wipe the hands
• but it naturally means wipe your hands here

Because the sentence is addressed to you, it is already clear whose hands are being talked about.

This is very common with body parts in Chinese:

• 抬头 = raise your head
• 闭上眼睛 = close your eyes
• 洗手 = wash your hands
• 张嘴 = open your mouth

You can say 擦一下你的手, but it is less natural in ordinary situations unless you want emphasis or contrast.

Yes, absolutely.

Both are natural:

• 请你用毛巾擦一下手。
• 请用毛巾擦一下手。

The version with 你 can feel a bit more direct toward the listener, as in please, you... But in many situations, Mandarin leaves out the subject when it is obvious.

So:

• 请用毛巾擦一下手。 = very natural
• 请你用毛巾擦一下手。 = also natural, slightly more explicitly directed at the listener

Neither is wrong.

It is a polite request, but the exact tone depends on context and voice.

Why it sounds polite:

• 请 softens it
• 一下 softens it further

So it is much gentler than just saying:

• 用毛巾擦手。

However, it can still function as an instruction, especially in places like:

• a restaurant
• a clinic
• someone’s home
• a classroom

So the tone is often:

• polite
• practical
• mildly directive

If you wanted to make it even softer, you could say things like:

• 请你用毛巾擦一下手，好吗？
• 麻烦你用毛巾擦一下手。

Yes. That is also grammatical:

• 请你用毛巾把手擦一下。

This uses the 把 construction, which brings the object 手 before the verb phrase:

• 把手擦一下 = wipe the hands

Both versions are natural:

• 请你用毛巾擦一下手。
• 请你用毛巾把手擦一下。

The 把 version can sound a little more focused on what is being done to the hands. The version without 把 is simpler and very common in everyday speech.

For learners, the original sentence without 把 is often easier to understand and use.

No measure word is needed here.

That is because 毛巾 is not being counted. It is simply the instrument introduced by 用:

• 用毛巾 = use a towel

Measure words are needed when you specify number:

• 一条毛巾 = one towel
• 这条毛巾 = this towel

But if you are just saying with a towel or use a towel, you can simply say:

• 用毛巾

So the sentence does not need:

• 用一条毛巾 unless you specifically mean use one towel
• 用这条毛巾 unless you mean use this towel

擦 is a flexible verb. Its meaning depends on context.

Common meanings include:

• to wipe
• to rub
• to clean by wiping
• sometimes to apply by rubbing

Examples:

• 擦桌子 = wipe the table
• 擦脸 = wipe your face
• 擦鞋 = polish / clean shoes
• 擦药 = apply medicine

So in 擦一下手, the natural meaning is wipe your hands.

The context created by 毛巾 makes that especially clear:

• 用毛巾擦一下手 = wipe your hands with a towel

Without context, 擦 can be broader, but here the meaning is very straightforward.