Мой брат умеет играть на гитаре.

Because брат is a masculine singular noun, and the possessive мой has to agree with it in gender, number, and case.

• мой = masculine singular
• моя = feminine singular
• моё = neuter singular
• мои = plural

So:

• мой брат = my brother
• моя сестра = my sister

In this sentence, брат is masculine, so мой is the correct form.

Брат is in the nominative case because it is the subject of the sentence — the person doing the action.

In Мой брат умеет играть на гитаре, the subject is мой брат.

So the structure is:

• Мой брат = subject
• умеет играть = predicate / verbal idea
• на гитаре = additional information about the instrument

Умеет comes from the verb уметь, which means to know how to do something or to be able to do something because you have learned the skill.

So умеет играть means:

• knows how to play
• is able to play in the sense of having the skill

This is different from simple physical possibility. It usually suggests learned ability or competence.

Examples:

• Я умею плавать. = I can swim / I know how to swim.
• Она умеет готовить. = She knows how to cook.

Because after уметь, Russian normally uses the infinitive.

So:

• умеет = knows how / is able
• играть = to play

Together:

• умеет играть = knows how to play

This is very similar to English can play or knows how to play.

Compare:

• Он играет на гитаре. = He plays the guitar.
• Он умеет играть на гитаре. = He knows how to play the guitar.

In the first sentence, играет is a finite verb.
In the second, играть is an infinitive used after умеет.

This is a very common question.

• уметь = to know how to, referring to skill, learned ability
• мочь = to be able to, referring to possibility, opportunity, permission, or capability in the moment

So:

• Мой брат умеет играть на гитаре. = My brother knows how to play the guitar.
• Мой брат может играть на гитаре. = My brother can play the guitar — but this could mean he is allowed to, has the opportunity to, or is physically able to right now.

In many situations, English can could match either one, but Russian often makes this distinction more clearly.

Yes, literally it looks like on the guitar, but this is just how Russian expresses playing a musical instrument.

Russian commonly uses:

• играть на + prepositional case

Examples:

• играть на гитаре = to play the guitar
• играть на пианино = to play the piano
• играть на скрипке = to play the violin

So although на often means on, in this construction you should learn it as a set pattern:

• играть на гитаре
• играть на фортепиано
• играть на трубе

It is not translated word-for-word into natural English.

Гитаре is in the prepositional case singular.

That is because of the pattern:

• играть на + prepositional

The noun гитара changes like this:

• nominative: гитара
• prepositional: на гитаре

So:

• гитара = the basic dictionary form
• на гитаре = on the guitar / on guitar, meaning on the instrument

This is one of those constructions that is best memorized as a whole phrase.

Russian has no articles — no a, an, or the.

So гитара can mean:

• a guitar
• the guitar
• just guitar

The exact meaning depends on context.

In this sentence, English naturally uses the guitar, but Russian simply says:

• на гитаре

without any article at all.

Yes. Russian word order is more flexible than English because case endings help show the grammatical roles.

The neutral order here is:

• Мой брат умеет играть на гитаре.

But other orders are possible, depending on emphasis:

• На гитаре мой брат умеет играть.
• Играть на гитаре мой брат умеет.

These alternatives are grammatically possible, but they sound more marked or emphasize different parts of the sentence.

For a learner, the standard neutral version is the best one to use first.

Yes, that is grammatically possible, but the meaning changes slightly.

• Мой брат умеет играть на гитаре. = My brother knows how to play the guitar.
• Брат умеет играть на гитаре. = Brother knows how to play the guitar or a brother knows how to play the guitar, depending on context

Russian often omits possessives when the relationship is already clear from context, but if you specifically want to say my brother, then мой is the normal choice.

You simply put не before умеет:

• Мой брат не умеет играть на гитаре.

This means:

• My brother does not know how to play the guitar.
• My brother can’t play the guitar in the sense of lacking the skill

This is the normal way to negate уметь.

A natural pronunciation is:

Мой брат уме́ет игра́ть на гита́ре.

Stress:

• мой — one syllable
• брат — one syllable
• уме́ет — stress on -ме́-
• игра́ть — stress on -ра́ть
• гита́ре — stress on -та́-

A rough pronunciation guide:

• мой ≈ moy
• брат ≈ braht
• уме́ет ≈ oo-MYE-yet
• игра́ть ≈ ee-GRAHT’
• на гита́ре ≈ na gee-TAH-rye

The unstressed vowels may sound weaker in natural speech, especially in faster pronunciation.

It normally expresses a general ability or skill, not an action happening at this moment.

So Мой брат умеет играть на гитаре means that your brother has learned this skill.

If you want to say he is playing right now, you would normally say:

• Мой брат играет на гитаре. = My brother is playing the guitar / plays the guitar.

So:

• умеет играть = has the skill
• играет = is playing / plays