Moj brat je visok.

Because brat is a masculine singular noun, and the possessive word moj has to agree with it.

• moj = my, for masculine singular nouns
• moja = my, for feminine singular nouns
• moje = my, for neuter singular nouns

So:

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

Je means is.

It is the 3rd person singular form of the verb biti (to be).

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In Moj brat je visok, je links my brother and tall, just like is in English.

In a sentence like this, standard Croatian normally does use the verb to be.

So:

• Moj brat je visok. = correct
• Moj brat visok. = not standard in normal Croatian

Croatian can sometimes omit parts of biti in certain styles or special contexts, but in an ordinary present-tense statement like this, je is expected.

Here visok is being used as a predicate adjective: it comes after je and describes the subject.

After to be, Croatian usually uses the short/indefinite adjective form:

• Brat je visok. = The brother is tall./My brother is tall.

The form visoki is the long/definite form, and it is more typical when the adjective comes before a noun:

• visoki brat = the tall brother

So in this sentence, visok is the natural form.

It can mean both, depending on context.

• Moj brat je visok. = My brother is tall
• Planina je visoka. = The mountain is high

So visok / visoka / visoko covers both ideas that English often separates into tall and high.

Croatian has no articles like English a/an/the.

So brat can mean:

• brother
• the brother
• sometimes just brother depending on context

In this sentence, moj brat already clearly means my brother, so no article is needed.

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

The basic structure is:

• Moj brat = subject
• je = verb
• visok = description of the subject

The nominative singular form is brat.

Yes. Croatian adjectives agree with the noun they describe in gender, number, and often case.

Since brat is:

• masculine
• singular
• nominative

the adjective is also:

• visok = masculine singular nominative

Compare:

• Moj brat je visok. = My brother is tall.
• Moja sestra je visoka. = My sister is tall.
• Moje dijete je visoko. = My child is tall.

Yes, Croatian word order is more flexible than English, although Moj brat je visok is the most neutral and natural version.

You may also hear:

• Brat mi je visok.

This also means My brother is tall, but the structure is a little different:

• brat = brother
• mi = to me / my, used here in a possessive way
• je = is
• visok = tall

This version is very common in everyday speech.

Je is pronounced roughly like ye in English, with j sounding like English y.

So:

• j in Croatian = y in yes
• je ≈ ye

That means:

• Moj sounds roughly like moy
• je sounds roughly like ye

Croatian has more than one way to express possession.

In this sentence:

• moj brat = my brother

But Croatian also often uses a dative clitic:

• Brat mi je visok.

Literally this is something like Brother to-me is tall, but naturally it means My brother is tall.

Both are correct. Very roughly:

• Moj brat je visok. = straightforward, neutral
• Brat mi je visok. = very natural in conversation

No, not exactly.

• Moj brat je visok. specifically means My brother is tall.
• On je visok. means He is tall.

Croatian usually states the noun directly if you want to say my brother, rather than replacing it with he unless the context is already clear.

You would change both the possessive form and the adjective form to match the feminine noun.

For example:

• Moja sestra je visoka. = My sister is tall.

Changes:

• moj → moja because sestra is feminine
• visok → visoka to agree with sestra

So agreement is very important in Croatian.