Лучше сохранять чек, пока действует гарантия.

Лучше here means it is better or better to. Russian often uses this kind of impersonal structure:

• Лучше + infinitive = It’s better to ...

So Лучше сохранять чек literally means Better to keep the receipt.

There is no subject like it in Russian here. English needs it’s, but Russian does not.

After лучше, Russian commonly uses the infinitive to express advice or a recommendation.

So:

• Лучше сохранять чек = It’s better to keep the receipt

This is a very common pattern:

• Лучше подождать = It’s better to wait
• Лучше проверить = It’s better to check

This is about aspect.

• сохранять = imperfective
• сохранить = perfective

In this sentence, сохранять sounds natural because the idea is to keep holding on to the receipt over a period of time, namely during the warranty period.

So the focus is not on one completed action, but on the ongoing state of keeping it.

Very roughly:

• Лучше сохранять чек, пока действует гарантия = Better to keep the receipt while the warranty is valid
• Лучше сохранить чек would sound more like better not throw it away / better make sure you keep it

Both can be possible in some contexts, but сохранять fits the idea of keeping something for as long as the warranty lasts.

Because чек is the direct object, so it is in the accusative case. But for an inanimate masculine singular noun, the accusative looks the same as the nominative.

So:

• nominative: чек
• accusative: чек

That is why there is no visible change.

Чек usually means receipt in everyday Russian.

Depending on context, it can also mean check in some financial contexts, but in a sentence about a warranty, it almost certainly means receipt.

That makes sense because a receipt is often needed for warranty service.

Here пока means while, as long as, or until depending on how you translate it into natural English.

In this sentence, the idea is:

• keep the receipt for the time during which the warranty is valid

So пока действует гарантия means something like:

• while the warranty is in effect
• as long as the warranty is valid
• until the warranty expires

The exact English wording can vary, but the Russian idea is the same.

Both word orders are possible:

• пока действует гарантия
• пока гарантия действует

Russian word order is more flexible than English. In this sentence, putting действует before гарантия sounds natural and slightly more fluid in this context.

So this is mainly a matter of style and information flow, not a change in basic meaning.

Действует literally means acts, functions, is in force, or is valid, depending on context.

With things like rules, tickets, offers, or warranties, it often means:

• is valid
• is in effect
• remains in force

So:

• действует гарантия = the warranty is valid / in effect

Because the verb действует is agreeing with гарантия.

• гарантия = singular noun
• действует = 3rd person singular

So grammatically, the warranty is the thing that is in effect.

In other words:

• пока действует гарантия = while the warranty is valid

Yes, you often can. Хранить чек also means to keep/store the receipt.

The difference is subtle:

• хранить = keep, store
• сохранять = preserve, keep, retain, save

In many everyday situations with documents or receipts, both may be understood. But сохранять чек is very common when the idea is don’t throw it away; keep it for later use.

Not exactly. It is more like advice or a recommendation.

• Сохраняйте чек would be a direct command or instruction: Keep the receipt
• Лучше сохранять чек is softer: It’s better to keep the receipt

So the sentence sounds helpful and practical rather than strictly imperative.

Yes. In Russian, the present tense is often used in clauses like this when talking about a period that is currently true or generally applies.

So even if the advice is about what you should do from now on, пока действует гарантия is still normal Russian.

It means the whole period during which the warranty is valid, whether that period started already or is still ongoing.