Моя подруга записалась на маникюр и купила красный лак для ногтей.

Because подруга is a feminine noun.

In Russian, possessive words like my change to match the gender of the noun:

• мой = my, for masculine nouns
• моя = my, for feminine nouns
• моё = my, for neuter nouns
• мои = my, for plural nouns

So:

• мой друг = my male friend
• моя подруга = my female friend

Not necessarily. Подруга usually means female friend.

Depending on context, it can sometimes be understood as girlfriend, but the basic meaning is simply a woman/girl friend. If the sentence is just talking about someone booking a manicure and buying nail polish, female friend is the most natural interpretation.

Compare:

• друг = male friend / friend
• подруга = female friend

The verb is записаться, which often means to sign up, to make an appointment, or to book oneself in.

The -ся / -сь ending is the reflexive marker. In this sentence, it shows that she made an appointment for herself.

So:

• записать = to write down / to register someone or something
• записаться = to sign up / make an appointment oneself

This is very common in Russian when talking about appointments:

• записаться к врачу = to make a doctor’s appointment
• записаться на маникюр = to book a manicure appointment

Because these are two different verbs in meaning:

• записала = she wrote down / recorded / registered something or someone
• записалась = she signed herself up / made an appointment

So:

• Она записала номер. = She wrote down the number.
• Она записалась на маникюр. = She booked a manicure appointment.

The reflexive form is necessary here because the subject is arranging the appointment for herself.

In Russian, записаться на is a standard pattern for booking an appointment for a service, treatment, class, or event.

So:

• записаться на маникюр = book a manicure
• записаться на массаж = book a massage
• записаться на курс = sign up for a course

This is just the normal preposition used with this meaning.

Also, after на here, маникюр is in the accusative case. Since маникюр is masculine and inanimate, its accusative looks the same as the nominative:

• nominative: маникюр
• accusative: маникюр

Because the subject, подруга, is feminine.

In the past tense, Russian verbs agree with the subject in gender and number:

• записался = he signed up
• записалась = she signed up
• записалось = it signed up
• записались = they signed up

The same thing happens with купила:

• купил = he bought
• купила = she bought

So both verbs show that the subject is feminine.

Because купила is perfective, and it presents the action as completed.

In this sentence, the idea is that she did buy the nail polish, as a finished event. That is why купить is used:

• купила = bought, completed action

By contrast:

• покупала = was buying / used to buy / bought (with focus on process or repetition)

So here, купила is the natural choice because the sentence lists two completed actions:

1. she booked a manicure
2. she bought red nail polish

Because лак is a masculine noun.

Adjectives in Russian must agree with the noun in gender, number, and case. The dictionary form of a masculine adjective is often -ый or -ий, so:

• красный = red, masculine
• красная = red, feminine
• красное = red, neuter
• красные = red, plural

Since лак is masculine, we say:

• красный лак = red nail polish

It is accusative, but for a masculine inanimate noun, the accusative form is the same as the nominative.

So:

• nominative: красный лак
• accusative: красный лак

That is why it looks unchanged.

Compare with a feminine noun:

• nominative: красная книга
• accusative: красную книгу

So the case is changing, but with лак the form happens to stay the same.

Literally, it means polish for nails.

• лак = lacquer / polish
• для = for
• ногтей = of nails

The preposition для always takes the genitive case, so ногти becomes ногтей.

Forms:

• nominative plural: ногти = nails
• genitive plural: ногтей = of nails

So:

• лак для ногтей = nail polish

This is a very common Russian way to build noun phrases:

• щётка для волос = hairbrush
• чашка для чая = teacup
• крем для рук = hand cream

Russian often leaves possession implicit when it is obvious from context.

In English, we often say for her nails, but Russian usually just says для ногтей = for nails / nail. It sounds natural and does not need a possessive.

If you really wanted to specify, you could say something like для её ногтей, but that would usually sound unnecessary here.

It can mean several related things, depending on context:

• a manicure as a beauty treatment
• a manicure appointment
• sometimes the result, like a person’s manicure

In записалась на маникюр, it clearly means a manicure appointment / service.

Russian often uses the name of the service itself after записаться на:

• на маникюр
• на педикюр
• на стрижку

Yes. Russian word order is fairly flexible.

The neutral order here is:

Моя подруга записалась на маникюр и купила красный лак для ногтей.

But other orders are possible, depending on emphasis:

• На маникюр моя подруга записалась и купила красный лак для ногтей.
• Красный лак для ногтей моя подруга купила и записалась на маникюр.

Those alternatives may sound more marked or emphasize a particular part of the sentence. The original version is the most neutral and natural for basic narration.

Yes, normally the sentence is understood as describing two completed actions, probably in sequence:

1. she booked a manicure
2. she bought red nail polish

The conjunction и simply means and, but because both verbs are perfective past forms, the sentence naturally sounds like a short chain of completed events.

A learner might find these useful:

• моя́
• подру́га
• записа́лась
• на
• маникю́р
• и
• купи́ла
• кра́сный
• лак
• для
• ногте́й

A few especially important ones:

• подру́га — stress on у
• записа́лась — stress on а
• маникю́р — stress on ю
• ногте́й — stress on the final е́й

Sometimes, but not always.

By itself, лак can mean lacquer, varnish, or polish, depending on context. To make it clear that it is nail polish, Russian often says:

лак для ногтей

In casual conversation, if the context is beauty products, a speaker might shorten it to just лак, but the full phrase is clearer for learners.