Learn Hardcore Russian: Музыкант репетирует вечером дома. - The musician rehearses at home in the evening.

An action happening now:
- Музыкант репетирует вечером дома.
  → The musician is rehearsing at home this evening. (if context is “right now / today”)
A habitual / regular action:
- Музыкант репетирует вечером дома.
  → The musician rehearses at home in the evenings. (general habit)

Russian uses the same present form for both “rehearses” and “is rehearsing”; the difference is shown by context or extra words like обычно (usually), сейчас (now), каждый вечер (every evening), etc.

How do you conjugate репетировать in the present tense?

Репетировать (to rehearse) is an imperfective verb. Present-tense forms are:

я репети́рую – I rehearse / I am rehearsing
ты репети́руешь – you rehearse (singular, informal)
он / она / оно репети́рует – he / she / it rehearses
мы репети́руем – we rehearse
вы репети́руете – you rehearse (plural or formal)
они репети́руют – they rehearse

In your sentence, музыкант is 3rd person singular, so the verb must be репетирует.

Why is it вечером and not вечер or в вечер?

Вечером is the instrumental case of вечер (evening), used adverbially to mean “in the evening”.

Russian often uses the instrumental case of time-of-day nouns as an adverb of time:

утром – in the morning
днём – in/at midday, in the daytime
вечером – in the evening
ночью – at night

You do not say в вечер for “in the evening”. You must use вечером.

So Музыкант репетирует вечером дома literally is like saying:
The musician rehearses, evening-ly, at home. → The musician rehearses at home in the evening.

What is the difference between вечером and по вечерам?

Both relate to “evening”, but they differ in how strongly they express repetition:

вечером – in the evening (on an evening / this evening / in the evening as a time of day)
- Can be one specific evening or a vague regular time, depending on context.
по вечерам – in the evenings (plural, regularly, as a rule)
- Strongly suggests a repeated, habitual action.

Compare:

Музыкант репетирует вечером дома.
→ He rehearses at home in the evening.
(Could be this evening, or a general statement; context decides.)
Музыкант репетирует по вечерам дома.
→ He rehearses at home in the evenings.
(Clearly a regular habit, repeated on many evenings.)

What exactly is дома, and how is it different from в доме?

Дома here is an adverb meaning “at home”.

It comes historically from the noun дом (house, home), but in modern usage:

до́ма (stress on the first syllable) = at home (adverb)
в доме = in the house / inside the building (literally: in the house)

So:

Музыкант репетирует вечером дома.
→ The musician rehearses at home in the evening.
Музыкант репетирует вечером в доме.
→ The musician rehearses in the house in the evening.
(More physical/locational: inside that building, not outdoors.)

There is also дома́ (stress on the last syllable), which is “houses” (nominative plural), but that is a different word and meaning.

Can the word order change? For example, can I say Вечером музыкант репетирует дома?

Yes. Russian word order is more flexible than English. Your basic sentence:

Музыкант репетирует вечером дома.

Possible variants (all grammatically correct):

Вечером музыкант репетирует дома.
Дома музыкант репетирует вечером.
Музыкант вечером репетирует дома.
Музыкант дома репетирует вечером.

All still mean roughly: The musician rehearses at home in the evening, but the emphasis shifts:

Starting with Вечером… highlights the time: In the evening, the musician rehearses at home (contrast with other times).
Starting with Дома… highlights the place: At home, the musician rehearses in the evening (maybe he performs elsewhere at other times).

The neutral, most typical order is close to what you have:
Subject – Verb – Time – Place: Музыкант репетирует вечером дома.

How would I say this in the past or future?

Starting from the present:

Музыкант репетирует вечером дома.
→ The musician rehearses / is rehearsing at home in the evening.

Past (imperfective, describing process or habit):

Музыкант репетировал вечером дома.
→ The musician rehearsed / was rehearsing at home in the evening.
(Can be a one-time past situation or a past habit, depending on context.)

Future (imperfective, focusing on process/habit):

Музыкант будет репетировать вечером дома.
→ The musician will be rehearsing / will rehearse at home in the evening.

Future (perfective, focusing on completion of one rehearsal):

Use a perfective partner like прорепетировать or отрепетировать:

Музыкант прорепетирует вечером дома.
→ The musician will rehearse (will get a rehearsal done) at home in the evening.

Imperfective = process / repeated activity; perfective = single, completed event.

Could I say Музыкант играет вечером дома instead of репетирует? What’s the difference?

You can say Музыкант играет вечером дома, but the nuance changes:

репетировать
- to rehearse; to practice a piece or program, often for a performance, concert, play, etc.
- sounds like structured practice, working on something specific.
играть (на пианино, на гитаре, и т.д.)
- to play (an instrument, a piece of music, or a game).
- more general: he plays music; may or may not be serious practice.

So:

Музыкант репетирует вечером дома.
→ He is rehearsing (seriously practicing, probably preparing something).
Музыкант играет вечером дома.
→ He plays (music) at home in the evening.
(He might just be playing for fun or generally performing, not necessarily rehearsing for something.)

How do I pronounce the sentence, and where is the stress?

Stresses (marked with capital letters) and rough pronunciation:

Музыка́нт – mu-zy-KANT
- stress on -кант: музыка́нт
репети́рует – re-pe-TEE-ru-yet
- stress on -ти́-: репети́рует
ве́чером – VYE-che-rom
- stress on ве́-: ве́чером
до́ма – DO-ma
- stress on до́-: до́ма (at home)

Full sentence with stresses:

Музыка́нт репети́рует ве́чером до́ма.

Note: in normal Russian writing, stress is usually not marked; you just learn it with the word.