В этой булочной по выходным часто продают ватрушку, бублик и сладкую слойку.

Because в here means in, describing a location, and Russian normally uses the prepositional case after в for location.

Base form:

• эта булочная = this bakery

In the sentence:

• в этой булочной = in this bakery

So both words change to match the prepositional case:

• эта → этой
• булочная → булочной

This is very common:

• в этом магазине = in this store
• в этой школе = in this school

По выходным means on weekends or at weekends.

This is a very common Russian time expression:

• по утрам = in the mornings
• по вечерам = in the evenings
• по выходным = on weekends

Here по is used with the dative plural, and выходным is the dative plural form of выходной.

So literally it is something like on the weekend-days / during weekends, but the natural English translation is simply on weekends.

Also, this expression usually suggests a repeated habit, not just one specific weekend.

Russian often uses the 3rd person plural with no subject to make an indefinite-personal statement.

So:

• продают literally = they sell
• but it really means people sell, they sell, or in natural English often is sold / are sold

In this sentence, the focus is not on who sells the pastries. The point is just that this is what happens there.

So:

• В этой булочной... продают...
  means something like
• At this bakery, they often sell... or
• ...is often sold...

This structure is extremely common in Russian.

Not necessarily. In Russian, the present tense of an imperfective verb often describes a habitual or repeated action, not only something happening right this moment.

Because the sentence also has:

• по выходным = on weekends
• часто = often

the meaning is clearly habitual:

• On weekends, they often sell...

So продают here means they regularly sell / they tend to sell, not necessarily they are selling at this exact moment.

Because the sentence describes a repeated, ongoing pattern, not a single completed sale.

• продавать / продают = imperfective, used for process, repetition, habit
• продать / продадут = perfective, used for a completed act

Here the idea is:

• they often sell these items on weekends

That is exactly the kind of situation where Russian prefers the imperfective.

If you used a perfective form, it would sound more like a specific completed event or result, which would not fit часто and по выходным as well.

They are the direct objects of продают, so they are in the accusative case.

Here is what happens:

• ватрушка → ватрушку
  feminine singular, accusative

• бублик → бублик
  masculine singular, inanimate; for inanimate masculine nouns, the accusative is usually the same as the nominative

• сладкая слойка → сладкую слойку
  both the adjective and noun change to accusative feminine singular

So the sentence is showing standard object case forms after the verb to sell.

Because the adjective has to agree with the noun it describes.

The base phrase is:

• сладкая слойка = a sweet puff pastry

But in the sentence, слойка is a direct object, so it becomes accusative:

• слойка → слойку

The adjective must match that:

• сладкая → сладкую

So:

• сладкую слойку = accusative feminine singular

This kind of agreement is one of the most important patterns in Russian grammar.

In Russian, singular nouns can be used when listing product types or items sold by piece, almost like naming entries on a menu or in a display.

So:

• продают ватрушку, бублик и сладкую слойку

can sound like:

• they sell vatrushka, bublik, and sweet puff pastry as items

Russian is not always focusing on number in exactly the same way English does in this kind of list.

That said, a plural version would also be possible:

• продают ватрушки, бублики и сладкие слойки

The plural version would feel a bit more like talking about those pastries as classes of goods in general. The singular version can feel a bit more like naming individual sale items.

That is a very normal position for an adverb of frequency in Russian.

• часто продают = often sell

Russian word order is flexible, so you could move часто, but the current placement is very natural and neutral.

For example:

• В этой булочной по выходным часто продают...
• По выходным в этой булочной часто продают...

Both are possible.

Putting часто before the verb is one of the most common patterns.

It can definitely be changed. Russian word order is much more flexible than English word order because the case endings already show the grammatical roles.

This sentence starts with background information:

• В этой булочной = place
• по выходным = time

Then it gives:

• часто продают = what usually happens

And finally:

• the items being sold

That is a very natural information flow: where → when → what happens → what is sold.

But other orders are also possible, especially for emphasis:

• По выходным в этой булочной часто продают...
• Часто по выходным в этой булочной продают...

The original order sounds neutral and smooth.

Because Russian has no articles.

Russian does not have direct equivalents of English a/an and the. Instead, definiteness is understood from context or shown in other ways.

For example:

• этой already helps make булочной definite: this bakery
• the pastry nouns are understood from context as the items being sold there

So Russian speakers do not need articles to make the sentence natural.

Булочная usually means a bread shop / bakery shop, a place where baked goods are sold.

Traditionally:

• булочная emphasizes the shop
• пекарня emphasizes the bakery as a place where things are baked

In modern usage, the difference is not always strict, and пекарня can also mean a bakery shop or bakery-café. But булочная strongly suggests a place selling bread, buns, and pastries.

So in this sentence, булочная fits very well.

This is standard Russian punctuation for a simple list.

The items are:

• ватрушку
• бублик
• сладкую слойку

Russian, like English, normally separates list items with commas, but does not put a comma before the final и in a simple list.

So:

• ватрушку, бублик и сладкую слойку

is exactly what you would expect.