На этой блузке снова появилась складка, потому что она весь день лежала в сумке.

Because here на means on in the sense of location, not motion.

• на этой блузке = on this blouse → location → prepositional case
• на эту блузку would mean onto this blouse or to this blouse → motion toward a surface → accusative case

In this sentence, the wrinkle is located on the blouse, so Russian uses the prepositional:

• на этой блузке

They are both in the prepositional singular feminine, but nouns and adjectives/pronouns decline differently.

• блузка → на блузке
• эта → на этой

So the endings are different because:

• блузка is a noun
• эта is a demonstrative pronoun/adjective

This is normal in Russian: words agree in case, number, and gender, but they do not always take the same ending.

Because складка is the subject of the verb появилась.

Literally, the structure is:

• A wrinkle appeared on this blouse again

So:

• складка = subject → nominative case
• появилась agrees with it in gender and number:
  • feminine singular subject → появилась

If you used складку, that would be accusative, which would make it a direct object, and that would not fit this verb.

Because появилась means appeared / showed up / formed, which matches the idea that the wrinkle was not there before and then became visible again.

Compare:

• На этой блузке снова появилась складка
  = A wrinkle appeared on this blouse again
• На этой блузке была складка
  = There was a wrinkle on this blouse

So появилась emphasizes the wrinkle’s coming into existence / becoming noticeable, not just its existence.

Because it agrees with складка, which is a feminine singular noun.

In the past tense, Russian verbs change for:

• gender in the singular
• number

So:

• masculine: появился
• feminine: появилась
• neuter: появилось
• plural: появились

Since складка is feminine singular, the verb is появилась.

It refers to блузка (the blouse), not складка (the wrinkle).

Why? Because the second clause says:

• она весь день лежала в сумке
  = it was lying in the bag all day

A blouse can lie in a bag all day. A wrinkle normally would not be described that way in this context.

So the logic is:

• A wrinkle appeared on the blouse again
• because the blouse had been in the bag all day

Even though both блузка and складка are feminine, context makes the meaning clear.

Because лежала agrees with она, and она refers to блузка, which is feminine.

So:

• блузка → feminine
• она → feminine pronoun
• лежала → feminine singular past tense

Also, лежать means to lie / to be lying, often for something resting somewhere horizontally or simply being placed somewhere.

So лежала в сумке means:

• was lying in the bag
• more naturally in English: had been in the bag

Because the sentence describes an ongoing state over a period of time: the blouse was lying in the bag all day.

Russian normally uses the imperfective for:

• ongoing situations
• repeated actions
• background description

So:

• лежала весь день = was lying all day / had been lying all day

A perfective form would suggest a completed event with different nuance, which is not what this sentence needs. The point here is the duration and state, not a single completed action.

Because Russian often uses the accusative case of duration to express how long something lasted.

So:

• весь день = all day
• literally: the whole day

Other examples:

• всю ночь = all night
• всю неделю = all week
• весь год = all year

This is a very common pattern in Russian.

Because в сумке expresses location: the blouse was in the bag.

• в сумке = in the bag → location → prepositional case
• в сумку = into the bag → motion/direction → accusative case

Here the blouse is already inside the bag, so Russian uses:

• в сумке

Снова means again. It tells us that this is not the first time the blouse has had a wrinkle.

So:

• появилась складка = a wrinkle appeared
• снова появилась складка = a wrinkle appeared again

You could leave it out, but then you would lose the idea of repetition.

Also, снова is often placed before the verb or near the part it modifies. Russian word order is flexible, so other placements are possible, but this one sounds natural.

Because потому что introduces a subordinate clause meaning because.

Russian normally puts a comma before subordinating conjunctions like:

• потому что = because
• когда = when
• если = if
• хотя = although

So the sentence is divided into:

1. На этой блузке снова появилась складка
2. потому что она весь день лежала в сумке

That is why the comma is required.

Yes. The best English translation depends on context.

For clothing, складка can mean:

• crease
• wrinkle
• sometimes fold

In this sentence, because the blouse was in a bag and got marked by being crumpled, wrinkle or crease is most natural.

A useful distinction:

• складка often refers to a fold or crease in fabric
• морщина usually means a wrinkle on skin or a face

So for clothes, складка is the right word here.

Russian word order is flexible, but the current order sounds natural and gives a clear flow:

• На этой блузке → topic/location
• снова появилась складка → what happened
• потому что она весь день лежала в сумке → explanation

You could rearrange parts of the sentence, but the emphasis would change. For example:

• Снова на этой блузке появилась складка...
• Складка снова появилась на этой блузке...

These are possible, but the original is a neutral, natural way to say it.

Russian often prefers a more concrete verb where English might use a more general one.

So English might say:

• it was in the bag all day

But Russian commonly says:

• она лежала в сумке весь день
• literally: it lay in the bag all day

This sounds normal and idiomatic in Russian. It gives a physical sense of the blouse being placed there, not just existing there abstractly.