Usitumie mkasi kukata nywele bila kuchana kwanza.

Because usitumie is a negative command: Don’t use.

It breaks down like this:

• u- = you (singular)
• -si- = negative marker
• -tumi- = verb root use
• -e = subjunctive ending, which is commonly used in commands and prohibitions

So usitumie means don’t use.

By contrast, hutumii means something like you do not use or you don’t use in a general statement, not a direct command.

It is the negative second-person singular imperative/prohibitive form.

In practical terms, learners often just think of it as:

• tumia! = use!
• usitumie! = don’t use!

If you were speaking to more than one person, or using plural/polite you, it would be:

• msitumie = don’t use (you all / you polite)

In Swahili, mkasi is the normal word for a pair of scissors / scissors. English treats scissors as grammatically plural, but Swahili does not have to match English grammar.

So:

• mkasi = scissors / a pair of scissors
• mikasi = plural, if you are talking about multiple pairs

This is a good example of how noun number does not always match between English and Swahili.

Kukata is the infinitive, meaning to cut.

After usitumie mkasi, the infinitive shows purpose:

• mkasi kukata nywele = scissors to cut hair
• or more naturally in English, scissors for cutting hair

So the structure is basically:

• Don’t use scissors [to cut hair]

Swahili often uses the infinitive this way after a noun or verb to show what something is for or what action follows.

Because Swahili often does not need an extra word like for in this structure.

English says:

• scissors for cutting hair
• use scissors to cut hair

Swahili can simply say:

• mkasi kukata nywele

The infinitive kukata already gives the idea of purpose, so no extra preposition is necessary.

Swahili does not have articles like the or a/an.

So nywele can mean:

• hair
• the hair
• your hair
• someone’s hair

The exact meaning depends on context.

If you wanted to be more specific, you could add a possessive:

• nywele zako = your hair
• nywele zake = his/her hair

But in this sentence, the general meaning is already clear, so nywele by itself is enough.

In this kind of sentence, nywele usually means hair as a collective noun, not separate individual hairs.

So even though English often treats hair as uncountable, Swahili uses nywele for hair in general, especially hair on the head.

If you are talking about a single strand of hair, that is different, but in everyday usage nywele is the normal word for hair.

Bila means without, and it is very commonly followed by an infinitive:

• bila kuchana = without combing
• bila kusema = without speaking
• bila kuona = without seeing

So here:

• bila kuchana kwanza = without combing first

This is a very useful pattern in Swahili:

• bila + infinitive

It could say kuchana nywele, and that would also be correct.

But the object is left out because it is already obvious from context. The sentence has just mentioned nywele, so when you hear kuchana, you naturally understand it as combing the hair.

So both are possible:

• bila kuchana kwanza
• bila kuchana nywele kwanza

The shorter version sounds natural because the listener already knows what is being combed.

Kwanza means first.

In this sentence, it tells you the order of actions:

• first comb
• then cut

So:

• bila kuchana kwanza = without combing first

It often comes after the verb phrase it modifies, so its position at the end is very natural.

The person being addressed by the command is understood as the one doing those actions.

So even though kukata and kuchana are infinitives and do not show a subject directly, the meaning is still:

• Don’t you use scissors to cut hair without first combing it

The subject is understood from usitumie, which is speaking directly to you.

Yes, that is possible, but it shifts the focus slightly.

• Usitumie mkasi kukata nywele... = Don’t use scissors to cut hair...
• Usikate nywele kwa mkasi... = Don’t cut hair with scissors...

These are very close in meaning, but the first one emphasizes using the scissors, while the second emphasizes the act of cutting.

So the original sentence is perfectly natural; it just frames the warning around the tool being used.

You would change usitumie to msitumie:

• Msitumie mkasi kukata nywele bila kuchana kwanza.

That means:

• Don’t use scissors to cut hair without combing first.
  addressed to you all or you in a polite/plural sense.