Usiweke karatasi hii kwenye mfuko; itakunjika.

Because Swahili negative commands use the negative subjunctive form. With kuweka (to put / place), the correct negative command to one person is usiweke.

Breakdown:

• u- = you (singular)
• -si- = negative
• weke = subjunctive form of weka

So usiweke means don’t put.
Usiweka is not the normal form here.

It is addressed to one person.

If you were speaking to more than one person, you would say msiweke.

Useful comparison:

• weka = put! (to one person)
• wekeni = put! (to several people)
• usiweke = don’t put! (to one person)
• msiweke = don’t put! (to several people)

In Swahili, demonstratives usually come after the noun, not before it.

So the normal pattern is:

• karatasi hii = this paper
• mfuko huu = this pocket / bag

That is why karatasi hii is the natural order.

Because karatasi belongs to noun class 9/10, and the demonstrative has to agree with that noun class.

For this class, the near demonstrative in the singular is hii.

You can see the same agreement again in the second clause:

• karatasi hii
• i-ta-kunjika

The i- in itakunjika also agrees with karatasi.

Kwenye is a very common locative word. Depending on context, it can mean in, into, on, or at.

With a verb like kuweka (to put), it often has the sense of into or in.

So kwenye mfuko means in the pocket or into the pocket.

Yes. Mfukoni is also very natural and means in the pocket.

So both of these work:

• kwenye mfuko
• mfukoni

The -ni ending makes a locative form. In everyday Swahili, both patterns are common.

Mfuko can mean pocket, bag, sack, or pouch, depending on context.

In this sentence, pocket is a very natural interpretation, because paper put there might get bent or creased. But the word itself is broader than just pocket.

It can be broken down like this:

• i- = subject marker agreeing with karatasi
• -ta- = future tense
• kunjika = become folded, bent, or creased

So itakunjika means it will get folded / bent / creased.

Because kunja is usually transitive: it means to fold something.

Example:

• Ninakunja karatasi. = I am folding the paper.

Kunjika is intransitive: it means to get folded, to become bent, or to become creased.

Example:

• Karatasi itakunjika. = The paper will get folded / creased.

So here the paper is not doing the folding to something else; it is the thing that will end up bent.

It can be broader than a neat, deliberate fold. In this context, it often suggests that the paper will get bent, creased, or folded up from being put in a pocket or bag.

So the idea is basically that the paper will not stay flat.

The semicolon links the warning to the result:

• Usiweke karatasi hii kwenye mfuko; itakunjika.

You could also say it as two separate sentences:

• Usiweke karatasi hii kwenye mfuko. Itakunjika.

Or you could make the reason more explicit:

• Usiweke karatasi hii kwenye mfuko kwa sababu itakunjika.

All of these are natural ways to express the same basic idea.