Moj brat čita brže nego ja.

Because moj has to agree with brat.

Brat is:

• masculine
• singular
• nominative here, because it is the subject

So the correct form is moj.

Compare:

• moj brat = my brother
• moja sestra = my sister
• moje dete = my child

It is in the nominative, because it is the subject of the sentence.

In Moj brat čita brže nego ja, the one doing the action is moj brat, so nominative is expected.

Čita is the 3rd person singular present tense form of the imperfective verb čitati.

So it matches moj brat:

• ja čitam = I read / I am reading
• ti čitaš = you read
• on / moj brat čita = he / my brother reads

Because čitati is imperfective, čita can mean either:

• reads in a general sense, or
• is reading, depending on context

In this sentence, the general meaning reads faster is the most natural.

Because brže is an adverb, while brži is an adjective.

Here the word describes how he reads, so it modifies the verb čita. That means Serbian uses an adverb:

• brzo = quickly / fast
• brže = more quickly / faster

By contrast:

• brži brat would mean a faster brother, where the word describes a noun

So:

• čita brže = reads faster
• brži brat = a faster brother

It is the comparative form of the adverb brzo.

• brzo = quickly, fast
• brže = faster, more quickly

Serbian comparatives are not all formed in exactly the same way, so it is best to learn them as patterns rather than expecting one single rule to work every time. But for this word, you should simply remember:

• brzo → brže

Nego means than in a comparison.

It introduces the second part of the comparison:

• Moj brat čita brže nego ja
• literally: My brother reads faster than I

In natural English, that is usually than I do.

Because the full meaning is really:

• Moj brat čita brže nego ja čitam

The second verb čitam is omitted because it is understood. Since ja is the subject of that implied verb, it stays in the nominative.

So:

• nego ja = than I do

This is similar to formal English than I rather than than me.

In everyday speech, you may sometimes hear other patterns, but in this structure nego ja is the standard form to learn.

Because Serbian often leaves out repeated words when they are obvious from context.

So these mean the same thing:

• Moj brat čita brže nego ja
• Moj brat čita brže nego ja čitam

The shorter version sounds natural and normal.

That is true: Serbian often leaves out subject pronouns because the verb ending already shows the person.

But pronouns are commonly kept when they are:

• contrasted
• emphasized
• clarified

Here ja is contrastive:

• my brother reads faster than I do

So it is very natural to include ja.

Sometimes yes, but nego is the better choice for this exact structure.

You may hear:

• Moj brat čita brže od mene

That is also understandable and common.

But nego ja more clearly matches the idea of a whole implied clause:

• than I do
• underlying form: nego ja čitam

A useful guideline is:

• use nego when the comparison feels like it includes another clause
• use od + genitive when comparing directly with a noun or pronoun

So for learners, Moj brat čita brže nego ja is an excellent model sentence.

No, Serbian word order is fairly flexible, but the given sentence is a very neutral and natural order.

You can also hear things like:

• Moj brat brže čita nego ja

That is also natural.

The original version:

• Moj brat čita brže nego ja

is a good standard word order for learners:

• subject
• verb
• comparative adverb
• comparison

A rough guide:

• č sounds like ch in church
• ž sounds like the sound in measure
• j sounds like y in yes

So:

• čita sounds roughly like CHEE-tah
• brže sounds roughly like BR-zheh

Also remember that Serbian spelling is very regular, so once you learn the letters, pronunciation becomes much easier.

Because Serbian does not have articles like English a and the.

So brat can mean:

• brother
• the brother
• a brother

The exact meaning depends on context.

In moj brat, the possessive moj already makes the noun definite enough, so English naturally uses my brother, but Serbian does not need an article at all.