Я читаю книгу, а мой брат в это время готовит ужин.

Читаю is the 1st person singular present-tense form of читать (to read).

• я читаю = I read / I am reading
• The ending -ю tells you the subject is я (I).

In Russian, the present tense is often used where English uses either:

• I read
• I am reading

So Я читаю книгу can mean I am reading a book in this context.

Because книга is the direct object of the verb читать (to read), it takes the accusative case.

• Nominative: книга = book (subject form)
• Accusative: книгу = book (object form)

So:

• Книга интересная. = The book is interesting.
• Я читаю книгу. = I am reading a book.

For many feminine nouns ending in -а, the accusative singular changes to -у.

Because мой must agree with the noun it describes.

Брат is:

• masculine
• singular

So the correct form is мой.

Compare:

• мой брат = my brother
• моя сестра = my sister
• моё письмо = my letter
• мои друзья = my friends

Russian adjectives and possessives change form to match the noun’s gender, number, and case.

Готовит is the 3rd person singular present-tense form of готовить (to prepare / to cook).

• я готовлю = I prepare
• ты готовишь = you prepare
• он / она готовит = he/she prepares

Since the subject is мой брат (my brother), Russian uses the 3rd person singular form:

• мой брат готовит = my brother is preparing / cooking

It can mean either, depending on context.

In this sentence, because it is happening at the same time as Я читаю книгу, the most natural English translation is:

• My brother is cooking dinner or
• My brother is preparing dinner

Russian present tense often covers both the simple present and the present continuous.

This is a very common question. А often connects two clauses that are contrasted, compared, or set side by side.

Here the sentence is not just saying and in a neutral way. It is more like:

• I am reading a book, while my brother, meanwhile, is cooking dinner.

So а works well because it highlights a parallel contrast between the two people and their actions.

Very roughly:

• и = and (simple addition)
• а = and / while / whereas / but depending on context
• но = but (stronger contradiction)

Here а is the natural choice.

В это время means at this time, at that time, or in this context meanwhile / at the same time.

In this sentence, it shows that the brother’s action is happening during the same period as the speaker’s action.

So:

• Я читаю книгу, а мой брат в это время готовит ужин. = I’m reading a book, and meanwhile my brother is cooking dinner.

It helps make the simultaneity clearer.

Because the expression в это время uses the accusative case, not the prepositional case.

This is because the phrase expresses a time span or time point in a fixed idiomatic way:

• в это время = at this time / during this time

Forms here:

• это is the accusative singular neuter form of этот
• время is neuter, and in this expression it stays время

Russian time expressions often do not match what an English speaker expects from the preposition alone.

Russian has no articles.

So:

• книга can mean a book or the book
• ужин can mean dinner, a dinner, or sometimes the dinner

You understand which one is meant from context.

In this sentence:

• читаю книгу is most naturally reading a book
• готовит ужин is most naturally cooking dinner

It actually is in the accusative case, but for this noun the accusative looks the same as the nominative.

Ужин is:

• masculine
• inanimate

For many masculine inanimate singular nouns, the:

• nominative = accusative

So:

• Nominative: ужин
• Accusative: ужин

That is why you do not see a change in form.

Compare:

• Я готовлю ужин. = accusative
• Ужин готов. = nominative

Same form, different grammatical role.

Yes, often it can be.

Russian frequently drops subject pronouns when the verb ending already makes the subject clear.

So:

• Я читаю книгу and Читаю книгу can both mean I am reading a book

However, in this sentence я is quite natural because:

1. it clearly introduces the speaker as one subject
2. the sentence contrasts I with my brother

So keeping я makes the comparison more explicit.

Here the verbs are imperfective:

• читать
• готовить

The imperfective aspect is used for:

• ongoing actions
• repeated actions
• general processes

In this sentence, the actions are presented as in progress at the same time, so imperfective is exactly what Russian needs.

If you used perfective verbs, it would sound wrong for this simultaneous ongoing situation, because perfective usually focuses on a completed result.

Yes, Russian word order is flexible.

This sentence uses a very natural order:

• а мой брат в это время готовит ужин

But you could also say:

• а в это время мой брат готовит ужин
• а мой брат готовит ужин в это время

The basic meaning stays similar, but the emphasis changes.

Commonly:

• в это время near the beginning gives it more prominence: meanwhile
• putting it later can sound a bit less smooth in this sentence

The version you were given is very natural and balanced.

Брат by itself just means brother.

It becomes my brother because of мой:

• брат = brother
• мой брат = my brother

Russian often uses possessives when English would too, especially in straightforward family references like this.

Yes. Готовить is a broad verb.

It can mean:

• to prepare
• to make ready
• to cook

So готовит ужин can be understood as:

• is cooking dinner
• is preparing dinner

In everyday context with ужин, cooking dinner is usually the most natural translation.

The original sentence is already natural and neutral.

A slightly simpler version could be:

• Я читаю книгу, а мой брат готовит ужин.

That drops в это время because the simultaneity is already clear from context.

Adding в это время makes the sentence feel a little more explicit:

• I’m reading a book, and meanwhile my brother is cooking dinner.

So the original is not strange at all—it just spells out the meanwhile / at the same time idea more clearly.