Khi tôi đau đầu, tôi thường uống nước và nghỉ một chút trước khi uống thuốc.

Khi means when. It introduces a time clause:

• Khi tôi đau đầu = When I have a headache

Putting it at the beginning is very natural in Vietnamese, just like starting an English sentence with When.... You could think of the structure as:

• Khi + clause, main clause
• When + clause, main clause

So here:

• Khi tôi đau đầu, tôi thường...
• When I have a headache, I usually...

In Vietnamese, đau đầu literally means head hurts or to have a headache. Vietnamese often expresses physical conditions this way, without needing a verb like have.

• đau = hurt / ache
• đầu = head

So:

• tôi đau đầu = I have a headache
• more literally: my head hurts

This is very common in Vietnamese:

• đau bụng = have a stomachache
• đau lưng = have back pain
• đau răng = have a toothache

The second tôi is there because Vietnamese often repeats the subject in the main clause after an introductory clause.

So the sentence is divided like this:

• Khi tôi đau đầu = when I have a headache
• tôi thường uống nước... = I usually drink water...

This repetition makes the sentence clear and natural. In English, we also do something similar:

• When I have a headache, I usually drink water...

You may sometimes hear subject omission in casual speech if the meaning is obvious, but repeating tôi here is normal and correct.

Thường means usually.

In Vietnamese, adverbs like thường often come before the main verb:

• tôi thường uống nước
• I usually drink water

So the pattern is often:

• subject + thường + verb

Examples:

• Tôi thường đi bộ. = I usually walk.
• Cô ấy thường ngủ sớm. = She usually sleeps early.

Yes, uống nước means drink water.

• uống = drink / take orally
• nước = water

In this sentence, it most naturally means drink water. Vietnamese often uses very direct everyday wording, so this is exactly what you would expect.

Also notice that uống is later used again in:

• uống thuốc = take medicine

Vietnamese uses uống for liquids and for medicine that is taken by mouth.

Nghỉ một chút means rest a little or rest for a bit.

• nghỉ = rest
• một chút = a little / a bit

Một chút softens the expression and makes it sound natural and conversational. It suggests a short amount of time or a small degree.

Examples:

• Đợi một chút. = Wait a moment.
• Nghỉ một chút. = Rest a bit.
• Ăn một chút thôi. = Just eat a little.

So here, nghỉ một chút means the speaker rests briefly before taking medicine.

Because Vietnamese usually expresses this idea with a full clause:

• trước khi = before
• uống thuốc = taking medicine

So:

• trước khi uống thuốc = before taking medicine

This is very natural Vietnamese. The structure is:

• trước khi + verb phrase
• before + verb-ing / before + clause

Examples:

• trước khi đi ngủ = before going to sleep
• trước khi ăn = before eating
• trước khi ra ngoài = before going out

Yes, thuốc means medicine. In Vietnamese, uống thuốc is the normal expression for take medicine when the medicine is swallowed.

• uống thuốc = take medicine orally
• literally: drink medicine

English uses take medicine, but Vietnamese uses a more physical verb based on how the medicine is consumed.

Related verbs:

• uống thuốc = take oral medicine
• bôi thuốc = apply medicine/ointment
• tiêm thuốc = inject medicine

So uống thuốc is completely natural here.

The sentence can be broken into three parts:

1. Khi tôi đau đầu = when I have a headache
2. tôi thường uống nước và nghỉ một chút = I usually drink water and rest a bit
3. trước khi uống thuốc = before taking medicine

So the full structure is:

• When + situation, subject + usually + action 1 + and + action 2 + before + action 3

In Vietnamese:

• Khi tôi đau đầu, tôi thường uống nước và nghỉ một chút trước khi uống thuốc.

The order is very logical and close to English.

It describes a habit or a usual routine.

The word thường tells you that this is something the speaker generally does, not just something happening once.

Vietnamese does not always mark tense the way English does. Instead, it often relies on context and time words.

Here:

• thường = usually
• therefore the sentence means a repeated habit

So it is best understood as:

• When I get a headache, I usually drink water and rest a bit before taking medicine.

Yes, but the meaning would change slightly.

With thường:

• Khi tôi đau đầu, tôi thường uống nước...
• When I have a headache, I usually drink water...

Without thường:

• Khi tôi đau đầu, tôi uống nước...
• When I have a headache, I drink water...

This is still grammatical, but thường makes the habitual meaning clearer and more natural if you want to talk about what you generally do.

Yes, in many contexts they are similar, but they are not exactly identical.

• một chút = a little / a bit
• một lát = a little while / a short time
• một lúc = a while / for a moment / for some time depending on context

In this sentence:

• nghỉ một chút sounds very natural
• nghỉ một lát also sounds natural
• nghỉ một lúc is possible, but can sound a bit longer or broader depending on context

So một chút is a very safe and common choice for rest a bit.

The comma is very natural and helpful because Khi tôi đau đầu is an introductory clause.

So:

• Khi tôi đau đầu, tôi thường uống nước...

This is similar to English writing:

• When I have a headache, I usually drink water...

In casual writing, Vietnamese punctuation can sometimes be flexible, but the comma is a good choice here and makes the sentence easier to read.