Learn Hardcore Russian: Музыкант любит этот инструмент.

Инструмент here is in the accusative case as a direct object, but for inanimate masculine nouns, the accusative form is identical to the nominative.

So:

Nominative: инструмент – instrument
Accusative (inanimate): инструмент – instrument (same form)

It is in the right case; it just looks the same as nominative because of this pattern in Russian grammar.

Why is it любит, not любить?

Любит is the 3rd person singular, present tense form of the verb любить (to love).

Conjugation of любить in the present tense:

я люблю – I love
ты любишь – you love (sg., informal)
он/она/оно любит – he/she/it loves
мы любим – we love
вы любите – you love (pl./formal)
они любят – they love

Because the subject is музыкант (he or she), we use любит.
Любить is the infinitive (to love), not used here.

What is the difference between любит and нравится? Could I say Музыканту нравится этот инструмент?

Both verbs express liking, but they work differently:

Любить = to love / to like (strongly) and it is a normal transitive verb:
- Музыкант любит этот инструмент. – The musician loves this instrument.
Нравиться = to be pleasing (to someone) and the person is in dative case:
- Музыканту нравится этот инструмент. – This instrument is pleasing to the musician (The musician likes this instrument).

Both sentences are grammatically correct, but:

любит is more personal/intense, emotional.
нравится is more neutral: finds it nice / likes it.

Why is it этот инструмент, not эта инструмент or этот инструмента?

The demonstrative этот / эта / это / эти must agree with the gender, number, and case of the noun.

инструмент is masculine singular, nominative/accusative.
The matching form is этот (masculine nominative/accusative singular).

So:

этот инструмент – this instrument (masculine)
эта книга – this book (feminine)
это окно – this window (neuter)
эти инструменты – these instruments (plural)

Инструмента would be genitive or accusative animate; not used here.

How do you pronounce Музыкант любит этот инструмент? Where is the stress?

Stress (marked with ´):

музыка́нт – mu-zy-KANT
лю́бит – LYU-bit
э́тот – E-tot
инструме́нт – in-stru-MYENT

Approximate IPA:

Музыкант: [mʊzɨˈkant]
любит: [ˈlʲubʲɪt]
этот: [ˈetət]
инструмент: [ɪnstrʊˈmʲent]

Sentence rhythm is fairly even:
Музыка́нт лю́бит э́тот инструме́нт.

Could the sentence mean “The musician is loving this instrument (right now)”?

Not exactly. Russian doesn’t have a separate continuous form like English (is loving).

Любит simply means “loves” or “likes” in a general or habitual sense:

Музыкант любит этот инструмент.
- Typically: The musician generally likes/loves this instrument.

Context can sometimes imply a current situation, but grammatically it’s simple present, not progressive.

Can word order be changed? For example: Этот инструмент музыкант любит?

Yes, Russian word order is more flexible than English, but changes often add emphasis or nuance.

Музыка́нт лю́бит э́тот инструме́нт.
- Neutral: The musician loves this instrument (standard order).
Э́тот инструме́нт музыка́нт лю́бит.
- Emphasis on этот инструмент: This instrument (as opposed to others) the musician loves.
Музыка́нт э́тот инструме́нт лю́бит.
- Emphasis on любит (not, for example, hates it).

The original sentence is the most neutral and natural for a beginner to use.

Why is there no word for “the” or “a” before музыкант or инструмент?

Russian has no articles (a, an, the).

Музыкант любит этот инструмент can mean:
- A musician loves this instrument
- The musician loves this instrument

Which one is meant is understood from context, not from a separate word.
The only explicit “this/that” here is этот = this.

Can музыкант refer to a woman, or do I need музыкантка?

Музыкант is grammatically masculine, but it can refer to any musician in a general or professional sense, male or female, especially in modern, neutral style.

Этот музыкант любит этот инструмент. – could be a man or a woman.

There is a specifically feminine form:

музыка́нтка – a female musician.

So if you really want to specify a woman, you can say:

Музыка́нтка лю́бит э́тот инструме́нт.

Does инструмент here only mean a musical instrument, or can it be a tool too?

Инструмент is a general word meaning “instrument” or “tool”, depending on context:

музыкальный инструмент – musical instrument
хирургический инструмент – surgical instrument
инструмент для ремонта – tool for repairs

In this sentence, because of музыкант, it naturally means musical instrument.

Can I say Музыкант любит играть на этом инструменте? How is it different?

Yes, that’s correct, and it’s a bit more specific.

Музыкант любит этот инструмент.
- The musician loves/likes this instrument (in general, as an object, its sound, etc.).
Музыкант любит играть на этом инструменте.
- The musician likes playing this instrument (emphasis on the activity).

Note: with musical instruments, Russian normally uses играть на + prepositional case:

играть на пианино, играть на гитаре, играть на этом инструменте.

Is любит perfective or imperfective? What would the perfective be?

Любит comes from любить, which is imperfective. It describes a state or repeated action (to love, to like).

There is no natural, widely used perfective partner that means “to love once / to start loving” in the same simple way. You might see:

полюбить – to come to love, to fall in love (start loving)

Example:

Музыкант полюбил этот инструмент. – The musician came to love this instrument / grew to love it.

But for general “loves/like”, you use the imperfective любить → любит.