На свадьбу она надела серёжки и браслет, а после ужина сняла их и убрала в косметичку.

Because на свадьбу uses the accusative case and expresses direction or purpose: to the wedding / for the wedding.

In this sentence, the idea is that she put the jewelry on for the wedding occasion.

Compare:

• на свадьбу = to/for the wedding
• на свадьбе = at the wedding

So:

• На свадьбу она надела серёжки = She put on earrings for the wedding
• На свадьбе она была в серёжках = She was wearing earrings at the wedding

Because после always takes the genitive case.

The noun ужин becomes ужина in the genitive:

• ужин = dinner
• после ужина = after dinner

This is a very common pattern:

• после работы = after work
• после фильма = after the movie
• после урока = after the lesson

This is a very common learner question.

In standard Russian:

• надеть = to put on an item of clothing/accessory
• одеть = to dress a person

So here надела серёжки и браслет is correct because she put on items.

Examples:

• надеть пальто = put on a coat
• надеть кольцо = put on a ring
• одеть ребёнка = dress a child

A useful memory trick is:

• надеть что-то
• одеть кого-то

Because earrings are normally thought of as a pair, so Russian often uses the plural, just like English often says earrings.

• серёжка = one earring
• серёжки = earrings

So она надела серёжки means she put on a pair of earrings.

Even if English sometimes focuses on the pair as one set, Russian still commonly uses the plural noun.

Because их refers to both objects together: серёжки и браслет.

Even though one noun is plural and the other is singular, together they form a plural group, so Russian uses the plural pronoun:

• серёжки и браслет → их

So:

• сняла их = took them off

This is exactly like English: the earrings and the bracelet ... she took them off.

Because these are past tense feminine singular forms.

The subject is она = she, so the past tense verbs agree with a feminine subject:

• он надел = he put on
• она надела = she put on
• он снял = he took off
• она сняла = she took off
• он убрал = he put away
• она убрала = she put away

In Russian past tense, gender matters in the singular.

Yes. These are perfective past forms, which present the actions as completed whole actions.

That fits the sentence well, because it tells a sequence of finished events:

1. She put them on
2. After dinner she took them off
3. She put them away in the cosmetic bag

The imperfective counterparts would be:

• надевала = was putting on / used to put on
• снимала = was taking off / used to take off
• убирала = was putting away / used to put away

Here the perfective forms are natural because the sentence is narrating completed actions.

Because в косметичку uses the accusative case and shows motion into something.

She put the jewelry into the cosmetic bag, so Russian uses:

• в + accusative for direction

Compare:

• убрала в косметичку = put it into the cosmetic bag
• лежит в косметичке = it is lying in the cosmetic bag

So:

• в косметичку = into the cosmetic bag
• в косметичке = in the cosmetic bag

Here убрала means something like put away, stored away, or put into its proper place.

It does not mean simply removed. That meaning is already expressed by сняла.

So the sequence is:

• сняла их = took them off
• убрала в косметичку = put them away into the cosmetic bag

This verb often has the sense of tidying something away:

• убрать книги в шкаф = put the books away in the cupboard
• убрать телефон в сумку = put the phone away in the bag

А here links the two parts of the sentence and creates a mild contrast or transition:

• first, she put the jewelry on for the wedding
• then, after dinner, she took it off and put it away

In English, this might be translated as and, but, or simply left as a pause depending on style.

Here а is very natural because it marks a shift to the next stage of the story.

Because in Russian, if the subject stays the same, it is often omitted in the next clause.

So after она надела..., it is already clear that the next actions were done by the same person. Russian therefore naturally says:

• ..., а после ужина сняла их...

instead of repeating она.

You could repeat it for emphasis, but it is usually unnecessary here.

They are in the accusative case, because they are the direct objects of надела.

For these particular nouns, the forms happen to look like the nominative:

• серёжки = nominative plural / accusative plural for inanimate nouns
• браслет = nominative singular / accusative singular for an inanimate masculine noun

So the forms do not visibly change here, but grammatically they are accusative.

The same is true in:

• сняла их → их is also the direct object

Russian word order is fairly flexible, but this version is very natural and neutral for storytelling.

The sentence structure is:

• На свадьбу = setting/purpose
• она надела серёжки и браслет = first completed action
• а после ужина = time marker for the next action
• сняла их и убрала в косметичку = second and third completed actions

You could rearrange parts for emphasis, for example:

• Она надела на свадьбу серёжки и браслет...
• После ужина она сняла их и убрала в косметичку

But the original version sounds smooth and idiomatic.

Because Russian, like English, usually replaces already mentioned nouns with a pronoun to avoid repetition.

So instead of saying:

• сняла серёжки и браслет и убрала серёжки и браслет в косметичку

Russian naturally says:

• сняла их и убрала в косметичку

This is more natural and less repetitive.

The main change would be in the past tense verb endings.

With она:

• надела
• сняла
• убрала

With он:

• надел
• снял
• убрал

So the sentence would become:

• На свадьбу он надел серёжки и браслет, а после ужина снял их и убрал в косметичку.

Grammatically this is fine, even if the situation is less typical.