Мастер быстро поменял ремешок, и сумочка снова стала удобной.

Because поменял is perfective, so it presents the action as completed: the repairman changed/replaced the strap and finished doing it.

• поменял = changed / replaced (completed action)
• менял = was changing / used to change / changed repeatedly (process or repeated action)

In this sentence, the result matters: after the strap was changed, the bag became convenient again. That is why the perfective verb fits well.

Ремешок is in the accusative case, because it is the direct object of поменял.

But it looks the same as the nominative because:

• it is masculine
• it is inanimate

For masculine inanimate nouns, nominative = accusative in the singular.

So:

• nominative: ремешок
• accusative: ремешок

Not usually in the English sense master. Here мастер means something like:

• repairman
• craftsman
• technician
• person who does this kind of work

In this context, it probably means someone at a repair shop who fixed the bag by replacing the strap.

Yes, both are diminutive forms.

• ремешок comes from ремень and means strap or little strap
• сумочка comes from сумка and means small bag / handbag / little bag

In Russian, diminutives are very common and do not always sound strongly emotional. They can simply sound more natural for small everyday objects.

So here:

• сумка = bag
• сумочка = handbag / small bag

And ремешок is a very normal word for a strap on a bag, watch, sandal, etc.

Because after стать meaning to become, Russian very often uses the instrumental case for the adjective.

So:

• стала удобной = became convenient / comfortable / practical

The adjective удобной is the instrumental feminine singular form of удобная.

This is a very important pattern:

• Он стал известным. = He became famous.
• Она стала счастливой. = She became happy.
• Сумочка стала удобной. = The bag became convenient.

Because the sentence describes a change of state.

• была удобной = was convenient
• стала удобной = became convenient

The meaning is: before the strap was changed, the bag was presumably not comfortable or practical to use; after the repair, it became convenient again.

Удобный is a very common Russian adjective, but it can cover several English ideas depending on context:

• comfortable
• convenient
• easy to use
• practical

For a bag, удобная often means something like:

• comfortable to carry
• practical to use
• easy to handle

So сумочка снова стала удобной could also be understood as:

• the handbag became practical again
• the bag was comfortable to use again

Yes, Russian word order is flexible, and снова can move around somewhat.

The sentence has:

• сумочка снова стала удобной

This is the most neutral order: the bag became convenient again.

You may also hear:

• сумочка стала снова удобной

That is possible, but it may sound a little less neutral in many contexts.

Russian word order often changes for emphasis, but the version in your sentence is very natural.

Russian often leaves possession implicit when it is obvious from context.

Here, once we hear about the strap and the handbag in the same sentence, we naturally understand that it is the bag’s strap.

English often prefers to make that relationship more explicit, but Russian does not always need to.

A fuller version could be something like:

• Мастер быстро поменял у сумочки ремешок...

But that sounds less neutral and is not necessary here.

Because стать is in the past tense, and in Russian past tense verbs agree with gender and number.

The subject is сумочка, which is:

• feminine
• singular

So the past tense form is:

• стал = masculine
• стала = feminine
• стало = neuter
• стали = plural

That is why the sentence says сумочка стала.

Yes, и means and, joining two clauses:

• Мастер быстро поменял ремешок
• и сумочка снова стала удобной

The second clause expresses the result of the first. So in English, depending on style, you could translate it as:

• The repairman quickly replaced the strap, and the handbag became practical again.
• The repairman quickly replaced the strap, so the handbag became usable again.

Russian uses simple и very often where English might sometimes prefer and, so, or and as a result.

Because that is a very normal position for an adverb in Russian.

• Мастер быстро поменял ремешок = The repairman quickly changed the strap

Russian adverbs are fairly flexible in position, but placing быстро before the verb sounds natural and neutral.

Other orders are possible for emphasis, for example:

• Мастер поменял ремешок быстро

But that can sound more marked, as if emphasizing quickly.

Not always, but it is very common in everyday Russian.

Поменять can mean:

• to change
• to replace
• to swap

In this context, поменял ремешок naturally means replaced the strap.

Another possible verb is заменить:

• Мастер быстро заменил ремешок

That also means The repairman quickly replaced the strap, and may sound a bit more formal or technical. Поменял is very natural in ordinary speech.

You could translate it literally that way, but it would sound unnatural in English.

The Russian diminutives ремешок and сумочка do not always need to be reflected in translation. A natural English translation would be more like:

• The repairman quickly replaced the strap, and the handbag became practical again.
• The repairman quickly changed the strap, and the bag was convenient to use again.

So when reading Russian, it is important not to over-translate diminutives word-for-word every time.