Моя сестра привела подругу на ужин, а потом ушла на тренировку.

Because сестра is a feminine noun, and the possessive pronoun my has to agree with it:

• мой = masculine
• моя = feminine
• моё = neuter
• мои = plural

So:

• мой брат = my brother
• моя сестра = my sister

Also, сестра here is in the nominative case because it is the subject of the sentence.

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

Here the subject is моя сестра, which is feminine singular, so the past-tense verbs take feminine forms:

• привёл / привела / привело / привели
• ушёл / ушла / ушло / ушли

So:

• сестра привела
• сестра ушла

If the subject were masculine, you would get:

• Мой брат привёл подругу... а потом ушёл...

Because подруга is the direct object of привела (brought), so it takes the accusative case.

For feminine nouns ending in -а, the accusative singular usually changes to -у:

• подруга → подругу
• сестра → сестру
• мама → маму

So:

• Она привела подругу = She brought a female friend

Привела is the past feminine singular form of привести.

In this context, привести means to bring someone somewhere, often with the sense of leading, accompanying, or bringing along a person.

That is why привести works well with people:

• привести друга
• привести ребёнка
• привести подругу

For objects, Russian more often uses other verbs, such as принести (bring, carrying something).

So:

• привела подругу = brought her friend along
• принесла книгу = brought a book

Because на + accusative is often used to show destination or purpose.

Here:

• на ужин = to dinner / for dinner
• на тренировку = to training / to practice / to a workout

This construction is very common:

• идти на работу = go to work
• поехать на концерт = go to a concert
• пригласить на ужин = invite to dinner

In на тренировку, the noun тренировка is feminine, so its accusative singular is тренировку.

Both can be possible in some contexts, but а often introduces a new step, contrast, or shift in the situation.

Here, а потом feels natural because the sentence moves from one completed action to another:

• she brought her friend over for dinner,
• and then / and after that she left for training.

So а потом often sounds like and then, sometimes with a slight sense of meanwhile / after that / next.

Very roughly:

• и = and
• а = and/but, with some contrast or change of scene

In this sentence, а потом is a very natural storytelling connector.

Both привела and ушла are perfective verbs:

• привести = to bring (completed)
• уйти = to leave/go away (completed)

Perfective is used because the sentence describes completed events in sequence:

1. she brought her friend for dinner,
2. then she left for training.

If you used imperfective verbs, the meaning would shift more toward process, repetition, or background action.

Compare:

• привела = brought, successfully arrived with
• ушла = left, went away

This is very typical in narration: perfective verbs show finished actions moving the story forward.

Grammatically, it is the sister.

The subject at the start is моя сестра, and no new subject is introduced after that. So the natural reading is:

• My sister brought her friend for dinner, and then my sister left for training.

Russian often omits repeated subjects when they are clear from context, just as English can do.

If the sentence meant that the friend left, Russian would usually make that clearer, for example by naming her again or changing the structure.

It can mean either, depending on context.

Most basically:

• друг = male friend
• подруга = female friend

But in real life, подруга can sometimes mean something closer to girlfriend, especially if the context suggests a romantic relationship.

In this sentence, the most neutral reading is simply female friend. Nothing in the sentence itself strongly forces the romantic meaning.

Yes. Russian word order is much more flexible than English word order because case endings show grammatical roles.

The sentence as given is neutral and natural:

• Моя сестра привела подругу на ужин, а потом ушла на тренировку.

But you could change the order to emphasize different things. For example:

• На ужин моя сестра привела подругу, а потом ушла на тренировку.
  This emphasizes for dinner.

• Моя сестра подругу привела на ужин...
  This can sound more marked, emphasizing the friend.

Even though word order can change, not every version sounds equally natural in every context. The original sentence is a good neutral default.

Russian does not have articles like English a/an and the.

So:

• сестра can mean a sister, the sister, or just sister, depending on context.
• подругу can mean a female friend or the female friend.

The listener figures out the meaning from context, word order, and what is already known in the conversation.

So in this sentence, Russian simply says:

• моя сестра = my sister
• подругу = a/the female friend

English has to choose an article, but Russian does not.

The stress is important:

• привела́
• ушла́

In both words, the stress is on the final -а.

A learner may expect stress earlier in the word, but here the stressed endings are normal:

• привела́
• ушла́

This also helps you sound more natural when reading the sentence aloud.