Она везёт сестру к врачу на машине, а по выходным часто возит детей в парк.

These are two forms from the pair везти / возить.

• везти → a specific trip, one direction, something happening right now or on one particular occasion
• возить → repeated, habitual, or back-and-forth transportation

So here:

• Она везёт сестру к врачу... = she is taking her sister to the doctor on this particular trip
• ...по выходным часто возит детей в парк = she often takes the children to the park as a regular activity

This is one of the classic Russian motion-verb distinctions that English usually does not show.

Not necessarily.

Везти / возить means to transport by vehicle. It focuses on the fact that someone is being taken somewhere using transport, not strictly on who is operating it.

In this sentence, на машине makes a car part of the situation, so the most natural interpretation is that she is driving them by car. But grammatically, the verb itself means to take/transport by vehicle, not specifically to drive.

Because they are direct objects, so they are in the accusative case.

• сестра → сестру
  Feminine singular nouns in -а usually change to -у in the accusative.

• дети → детей
  This is irregular, but it follows the rule that animate plural direct objects take the same form as the genitive plural.

So:

• Она везёт сестру = she is taking her sister
• возит детей = she takes the children

Since both refer to people, the animate-object pattern matters.

Russian uses different prepositions depending on the kind of destination.

• к + dative = to/toward a person or a person-centered destination
  So к врачу literally means to the doctor.

• в + accusative = into/to a place
  So в парк means to the park.

Also note the case change:

• врач → врачу after к
• парк → парк after в because masculine inanimate accusative looks like nominative

So the difference is not random; it reflects how Russian conceptualizes the destination.

Because на + prepositional is the normal Russian pattern for many means of transport.

Examples:

• на машине = by car
• на автобусе = by bus
• на поезде = by train
• на такси = by taxi

So на машине is simply the standard idiomatic way to say by car / in a car.

The noun changes like this:

• машина → машине

По выходным means on weekends or every weekend.

This uses a common Russian pattern:

• по + dative plural = repeated time periods

Examples:

• по выходным = on weekends
• по утрам = in the mornings
• по вечерам = in the evenings

So выходным is the dative plural form of выходные.

This pattern often gives the sense of whenever that time comes around regularly.

It can be translated as and, but here it does more than simply join two clauses.

А often introduces a contrast or comparison between two related facts.

In this sentence, it contrasts:

• what she is doing now / on this specific trip
• what she does habitually on weekends

So а is something like:

• while
• whereas
• and as for
• sometimes just and, but with a contrastive flavor

It is softer than но, which would sound more like a stronger but.

Yes, both verbs are in the present tense.

Russian present tense can cover both:

• an action happening right now
• a habitual action

The difference comes from context and verb choice:

• везёт suggests a specific trip in progress
• часто возит clearly means a repeated habit

So Russian does not need separate forms like English is taking vs takes. The meaning comes from the motion verb and time expressions such as по выходным and часто.

Yes, very often it could.

Russian frequently drops subject pronouns because the verb ending already shows the person and number:

• везёт = she/he is taking
• возит = she/he takes regularly

So in context, you might simply say:

• Везёт сестру к врачу...

But она is perfectly normal when:

• the speaker wants to make the subject clear
• the sentence begins a new topic
• there is a contrast with someone else
• the speaker wants a little emphasis

So the pronoun is optional in many situations, but not unnatural.

It is very important for pronunciation and stress.

• везёт has ё, and ё is always stressed
• so the stress is on the last syllable

Learners should pronounce it approximately as vye-ZYOT.

In many Russian texts, ё is often written as е, so you may see везет in ordinary writing. But the correct pronunciation is still везёт.

This matters because:

• stress changes meaning and pronunciation
• е and ё are not the same sound

So for learners, it is good to mentally restore ё whenever needed.

Because that is a very natural position for an adverb of frequency in Russian.

• часто возит детей в парк = she often takes the children to the park

Russian word order is fairly flexible, but the position before the verb is common and neutral for adverbs like:

• часто = often
• обычно = usually
• редко = rarely

You may see other word orders for emphasis, but часто возит is the most straightforward neutral version here.