Vaa jaketi la kujiokolea, la sivyo hutakuwa salama.

Vaa is the singular imperative of kuvaa, meaning to wear or to put on.

So in this sentence, Vaa! means Put on! / Wear!

Swahili often gives commands without a separate word for you, so vaa already implies you (singular).

It can mean either, depending on context.

• kuvaa nguo = to wear clothes / to put on clothes
• In a warning like this one, vaa jaketi la kujiokolea is most naturally understood as put on a life jacket

So English may choose wear or put on, but Swahili uses the same verb here.

Yes. Jaketi is a loanword from English jacket.

In this sentence it refers specifically to a life jacket, not just any jacket, because of the phrase la kujiokolea that follows it.

Because la agrees with the noun class of jaketi.

Here, jaketi is treated as a class 5 singular noun, so the connector is la.

A very literal breakdown is:

• jaketi = jacket
• la = of / for
• kujiokolea = saving oneself / self-rescue

So jaketi la kujiokolea is literally something like a jacket for saving yourself, which is how Swahili expresses life jacket here.

Kujiokolea means something like to save oneself or for self-rescue.

You can see these parts in it:

• ku- = infinitive marker, like to
• ji- = reflexive marker, meaning oneself / self
• the rest comes from the verb -okoa, meaning save or rescue

So the whole expression la kujiokolea describes the jacket by its purpose: it is a jacket used to save yourself.

Because Swahili does not use articles like English a, an, and the.

So:

• jaketi can mean a jacket, the jacket, or just jacket
• the exact meaning depends on context

That is very normal in Swahili.

La sivyo means otherwise, if not, or or else.

It is best learned as a fixed expression.

So:

• Vaa jaketi la kujiokolea, la sivyo hutakuwa salama.
• Put on a life jacket, otherwise you will not be safe.

Because it contains several grammatical pieces:

• hu- = you (singular, negative)
• -ta- = future marker
• kuwa = to be

So:

• utakuwa = you will be
• hutakuwa = you will not be

This is the normal negative future form for you (singular).

Because Swahili usually puts the subject inside the verb itself.

In this sentence:

• vaa already implies you (singular) as a command
• hutakuwa already includes you (singular) in hu-

You could add wewe for emphasis, but it is not necessary.

Salama means safe, secure, or out of danger.

In common use, salama is usually treated as an invariable word, so it stays salama rather than changing to match noun class.

That is why you get:

• nitakuwa salama = I will be safe
• watakuwa salama = they will be safe
• hutakuwa salama = you will not be safe

You would change the singular command and the singular future form to plural:

• Vaeni jaketi la kujiokolea, la sivyo hamtakuwa salama.

Changes:

• vaa → vaeni = wear/put on! (plural)
• hutakuwa → hamtakuwa = you all will not be

So that version means Put on life jackets, otherwise you all will not be safe.