В июне по четвергам моя подруга ходит на йогу после работы.

Because after в when talking about time such as a month, Russian usually uses the prepositional case.

• июнь = June
• в июне = in June

So в июне means in June.

This is very common:

• в январе = in January
• в мае = in May
• в сентябре = in September

Here июне is the prepositional form of июнь.

In this sentence, по means something like on in the sense of on Thursdays / every Thursday.

So:

• по четвергам = on Thursdays / every Thursday

This construction is very common for repeated actions on days of the week:

• по понедельникам = on Mondays
• по средам = on Wednesdays
• по пятницам = on Fridays

It shows a habitual, repeated schedule, not a one-time event.

Because after по in this meaning, Russian uses the dative case.

The singular noun is:

• четверг = Thursday

The plural is:

• четверги = Thursdays

But after по, it becomes dative plural:

• по четвергам

So the pattern is:

• по + dative plural for repeated days of the week

For example:

• по субботам = on Saturdays
• по воскресеньям = on Sundays

Because ходит is used for a repeated, habitual action, while идёт usually means someone is going right now in one direction.

In this sentence, the meaning is that your friend does this regularly:

• моя подруга ходит на йогу = my friend goes to yoga / attends yoga regularly

Compare:

• Моя подруга ходит на йогу по четвергам. = My friend goes to yoga on Thursdays.
• Моя подруга сейчас идёт на йогу. = My friend is going to yoga now.

So ходит is the correct choice because the sentence describes a routine.

Russian commonly uses ходить / идти на for going to an event, activity, class, lesson, concert, sport, or similar destination.

So:

• на йогу = to yoga / to a yoga class

This is the same pattern as:

• на работу = to work
• на концерт = to a concert
• на урок = to a lesson
• на тренировку = to training/practice

The idea is not really into yoga as a concept, but to a yoga session/class.

Because after verbs of motion like ходить when expressing destination with на, Russian uses the accusative case.

• йога = yoga
• на йогу = to yoga

So the pattern is:

• идти / ходить на + accusative

Examples:

• идти на работу
• ходить на курсы
• пойти на концерт

Since йога is a feminine noun ending in -а, its accusative singular is йогу.

After после meaning after, Russian uses the genitive case.

• работа = work
• после работы = after work

So работы is the genitive singular form.

This is a very common rule:

• после урока = after the lesson
• после обеда = after lunch
• после встречи = after the meeting

Because моя подруга is the subject of the sentence — the person performing the action.

• моя = my
• подруга = female friend

Since she is the one who goes, the phrase stays in the nominative case:

• моя подруга ходит... = my friend goes...

If she were an object, the form would change. But here she is the subject.

Yes, Russian word order is quite flexible, because case endings show grammatical roles.

The sentence:

• В июне по четвергам моя подруга ходит на йогу после работы.

is natural and emphasizes the time frame first:

1. В июне = in June
2. по четвергам = on Thursdays
3. моя подруга = my friend
4. ходит на йогу = goes to yoga
5. после работы = after work

You could also say:

• Моя подруга в июне по четвергам ходит на йогу после работы.

That is also correct. The difference is mostly one of emphasis and information flow, not basic meaning.

Yes. Подруга means a female friend.

Russian distinguishes:

• друг = male friend
• подруга = female friend

So if the speaker says моя подруга, the friend is female.

Also note that моя agrees with подруга, which is feminine singular.

They are very close in meaning, but not always identical in style.

• по четвергам = on Thursdays / every Thursday
• каждый четверг = every Thursday

In many sentences, either one works:

• Она ходит на йогу по четвергам.
• Она ходит на йогу каждый четверг.

A small difference:

• по четвергам sounds like a general recurring schedule
• каждый четверг can sound a little more explicit or emphatic: every single Thursday

Both are common and natural.

Several parts of the sentence signal repetition:

• по четвергам = on Thursdays
• ходит = goes regularly / habitually

Together they strongly show a routine:

• In June, on Thursdays, my friend goes to yoga after work.

If it were a single event, Russian would normally use different wording, often with a specific date or a verb form showing one trip/event.

For example, a one-time action might use пойдёт or идёт, depending on the context:

• В четверг моя подруга пойдёт на йогу. = On Thursday my friend will go to yoga.
• Моя подруга сейчас идёт на йогу. = My friend is going to yoga now.