Вчера её кудри держались до вечера, потому что маленькая заколка хорошо держала волосы.

Here её means her.

In её кудри, it shows possession: her curls.
Russian often uses the same form её for:

• her as a possessive: её волосы = her hair
• her as an object: я вижу её = I see her

So in this sentence, её is best understood as a possessive word meaning her.

A useful thing to remember: Russian possessive words like мой, твой, наш usually change endings, but её, его, их do not change.

Кудри means curls, and it is plural here. Since the subject is plural, the verb must also be plural.

So:

• кудри = plural noun
• держались = past tense, plural

In the Russian past tense, verbs agree with the subject in number and, in the singular, also in gender.

Compare:

• кудри держались = the curls held/stayed
• локон держался = the curl held/stayed

The ending -лись shows:

• -ли- = plural past
• -сь = reflexive marker

Держались comes from держаться.

That reflexive verb often means things like:

• to stay in place
• to hold up
• to last
• to remain fixed

So here её кудри держались до вечера means something like:

• her curls stayed in place until evening
• her curls held up until evening

It is reflexive because Russian uses держаться when the thing itself remains in place, rather than someone actively holding it.

Compare:

• заколка держала волосы = the hairpin held the hair
• кудри держались = the curls held / stayed in place

So the reflexive form changes the meaning from holding something to staying held / staying in place.

They are related, but not identical.

• держать = to hold something
• держаться = to hold/stay in place, to last

So:

• заколка хорошо держала волосы
  = the hairpin held the hair well

• кудри держались до вечера
  = the curls stayed in place until evening

This is very natural in Russian. English would often avoid repeating hold, but Russian is perfectly happy to use these related forms in the same sentence.

Because the preposition до requires the genitive case.

So:

• вечер = nominative
• до вечера = genitive after до

This pattern is very common:

• до утра = until morning
• до дома = as far as the house / until the house
• до конца = until the end

So до вечера literally means until evening.

Because маленькая заколка is the subject of the second clause.

In маленькая заколка хорошо держала волосы, the hairpin is the thing doing the action, so it stays in the nominative:

• маленькая заколка = nominative singular feminine

If it were the object, then you would get:

• я вижу маленькую заколку = I see a small hairpin

So here the nominative is correct because the hairpin is the subject.

Because its subject, заколка, is feminine singular.

In the Russian past tense:

• masculine singular often ends in -л
• feminine singular in -ла
• neuter singular in -ло
• plural in -ли

So:

• заколка держала = feminine singular
• кудри держались = plural

This is one of the most important things to notice in Russian past-tense verbs: they show agreement with the subject.

Because хорошо is an adverb, and it modifies the verb держала.

It means well:

• хорошо держала волосы = held the hair well

By contrast, хорошая is an adjective and would describe a noun:

• хорошая заколка = a good hairpin

So:

• маленькая заколка = adjective + noun
• хорошо держала = adverb + verb

That is a very common difference between Russian and English.

In Russian, волосы is normally plural when talking about the hair on someone’s head:

• у неё длинные волосы = she has long hair
• мыть волосы = to wash one’s hair

The singular волос usually means a single hair.

So in this sentence:

• заколка хорошо держала волосы = the hairpin held her hair well

Even though English often uses singular hair, Russian normally uses plural волосы.

Because потому что introduces a subordinate clause, like because in English.

The sentence has two parts:

1. Вчера её кудри держались до вечера
2. потому что маленькая заколка хорошо держала волосы

Russian normally separates this kind of clause with a comma.

So the comma here is standard punctuation.

Yes, потому что is a very common and neutral way to say because.

It is used all the time in everyday speech and writing.

You may also see other ways to express cause, such as:

• так как = since / because
• из-за того что = because of the fact that
• ведь = often something like after all / you see

But for a straightforward sentence like this, потому что is exactly what learners should expect.

Yes, Russian word order is fairly flexible.

This sentence uses a very natural, neutral order:

• Вчера sets the time first
• then comes the main idea
• then the reason with потому что

You could change the order for emphasis, for example:

• Её кудри вчера держались до вечера...
• Потому что маленькая заколка хорошо держала волосы, её кудри держались до вечера.

These versions are possible, but the original sounds very normal and straightforward.

So the given order is not the only one possible, but it is a natural default.

Ё represents a yo sound, and in careful writing it is written as ё.

So:

• её is pronounced with ё
• it is sometimes written as ее in ordinary texts, because Russian often omits the dots over ё

However, writing её with ё is very helpful for learners and is considered fully correct.

So you may see both:

• её
• ее

They mean the same thing here, but её is clearer.