Muzica deranjează copilul.

Because Romanian usually puts the definite article at the end of the noun instead of using a separate word before it.

So:

• muzica = the music
• copilul = the child

This is one of the biggest differences from English word structure.

These are the definite singular forms of the nouns:

• muzică = music
• muzica = the music
• copil = child
• copilul = the child

The endings are different because the nouns belong to different genders:

• muzică is feminine, so the definite ending here is -a
• copil is masculine, so the definite ending is -ul

So the sentence uses two definite nouns: the music and the child.

The dictionary forms are:

• muzică = music
• a deranja = to bother / to disturb / to annoy
• copil = child

In the sentence, those appear as:

• muzica = definite form of muzică
• deranjează = conjugated verb form of a deranja
• copilul = definite form of copil

Deranjează is the present tense, 3rd person singular form of a deranja.

It is used with:

• el = he
• ea = she
• it
• any singular noun subject, such as muzica

So muzica deranjează means the music bothers or, depending on context, the music is bothering.

In this sentence, the most natural reading comes from word order:

• Muzica comes before the verb, so it is understood as the subject
• copilul comes after the verb, so it is understood as the direct object

So the meaning is:

• The music bothers the child

This matters because Romanian nouns often have the same form for nominative and accusative, so you cannot always tell only from the noun ending.

If you reverse the order:

• Copilul deranjează muzica

that would mean The child bothers the music, which is grammatically possible but semantically odd.

Romanian often uses the simple present where English may use either:

• bothers
• is bothering

So Muzica deranjează copilul can mean:

• The music bothers the child
• The music is bothering the child

The exact English translation depends on context.

You may also hear a version like:

• Muzica îl deranjează pe copil.

This is very common when the direct object is a person.

What is happening there:

• pe copil marks the child more clearly as the direct object
• îl repeats that object with a clitic pronoun

Your original sentence, Muzica deranjează copilul, is understandable and grammatical, but Muzica îl deranjează pe copil often sounds more explicit and more natural in everyday Romanian when the object is human.

Yes. Romanian word order is more flexible than English, though different orders can change the focus or emphasis.

For example:

• Muzica deranjează copilul. = neutral order
• Pe copil îl deranjează muzica. = emphasizes the child

Both can express the same basic idea, but the second one highlights who is affected.

No. ă is not a stress mark. It is a different vowel letter in Romanian.

It represents a short, neutral sound similar to the a in about.

So in deranjează, the final ă is just part of the spelling and pronunciation. Romanian normally does not mark stress in ordinary writing.

A rough pronunciation guide is:

• Muzica ≈ MOO-zi-ka
• deranjează ≈ de-ran-ZHEA-zə
• copilul ≈ ko-PEE-lul

A few useful points:

• j in Romanian sounds like the s in measure
• ă sounds like the a in about
• the stress is roughly on MU in muzica, ZHEA in deranjează, and PI in copilul

So the whole sentence is approximately:

MOO-zi-ka de-ran-ZHEA-zə ko-PEE-lul