По выходным моя сестра играет в теннис, а её ракетка всегда лежит в машине.

По выходным is a common Russian way to say on weekends in the sense of a repeated habit.

• по here takes the dative
• выходным is dative plural
• literally, it comes from the idea of on weekend days

So По выходным моя сестра играет в теннис means My sister plays tennis on weekends / every weekend.

This phrasing usually suggests a regular pattern, not just one specific weekend.

Both can be translated as on the weekend / on weekends, but they are used a little differently.

• по выходным strongly suggests a habitual, repeated action: on weekends, as a rule
• на выходных is often more colloquial and can refer to this weekend / over the weekend or sometimes weekends in general, depending on context and region

So in this sentence, по выходным is especially natural because the sentence describes what the sister usually does.

Russian uses the present tense of an imperfective verb to talk about:

• habits
• routines
• repeated actions
• general facts

So играет here does not mean only is playing right now. It means plays in the habitual sense.

In this sentence:

• моя сестра играет в теннис = my sister plays tennis
• together with по выходным, it clearly means she does this regularly

After играть when you mean play a game or sport, Russian normally uses в + accusative.

So:

• играть в теннис = play tennis
• играть в футбол = play football/soccer
• играть в шахматы = play chess

Here теннис is in the accusative, but because it is an inanimate masculine noun, its accusative form looks the same as the nominative: теннис.

Compare this with other meanings of играть:

• играть на гитаре = play the guitar
• играть с детьми = play with children

А often links two clauses with a contrast or a switch of topic. It can be translated as:

• and
• while
• whereas
• but

depending on context.

In this sentence, а is not a strong contradiction. It is more like:

• My sister plays tennis on weekends, and her racket always lies in the car
• or ..., while her racket always stays in the car

So а shows a relationship between the two parts, with a slight contrast between the sister and the racket.

Here её means her and functions as a possessive:

• её ракетка = her racket

A useful thing to know: её does not change form the way мой / моя / моё / мои do.

So you get:

• её брат = her brother
• её сестра = her sister
• её ракетка = her racket

Also, её can sometimes mean her as an object pronoun, but here it is clearly possessive because it comes before a noun.

One more note: in many texts, you may see ее written without the dots, but it is still often pronounced as её.

Russian often uses position verbs where English simply uses is.

Common ones are:

• лежать = lie
• стоять = stand
• висеть = hang

So ракетка лежит в машине literally means the racket is lying in the car.

This is very natural in Russian. It tells you how the object is situated. A racket in a car is naturally imagined as lying there.

You could say находится instead, but that is more neutral or formal:

• её ракетка находится в машине

That sounds more like her racket is located in the car.

Russian usually does not use a present-tense verb equivalent to English is for this kind of location sentence.

Here в means in, and because the racket is located inside the car, Russian uses the prepositional case.

• машина = car
• в машине = in the car

So машине is prepositional singular.

A very important contrast:

• в машине = in the car, inside the car already
• в машину = into the car, movement toward the inside of the car

So:

• ракетка лежит в машине = the racket is in the car
• она кладёт ракетку в машину = she puts the racket into the car

Russian punctuation is stricter than English in many places. When two clauses with their own verb are joined by a conjunction like а, a comma is normally used.

Here the sentence has two clauses:

• По выходным моя сестра играет в теннис
• её ракетка всегда лежит в машине

Each clause has its own subject and verb:

• сестра играет
• ракетка лежит

So the comma before а is standard and expected.

The word order is natural, and it highlights the information in a useful way.

• По выходным is placed first to set the time frame: as for weekends
• моя сестра then introduces the subject
• всегда comes before лежит, which is a very normal position for an adverb like always

Russian word order is more flexible than English because case endings show grammatical roles. That means the sentence could be rearranged in other ways, but the given version sounds neutral and natural.

For example:

• По выходным моя сестра играет в теннис = neutral, good topic-first structure
• Её ракетка всегда лежит в машине = also neutral and natural

Russian has no articles like English a / an / the.

So:

• моя сестра can mean my sister
• её ракетка can mean her racket
• в машине can mean in the car or in a car, depending on context

In this sentence, context makes the meaning definite:

• my sister
• her racket
• the car or the car she uses / the family car, depending on the situation

Russian relies on context, word order, and general meaning instead of articles.