Ako ti zatreba pomoć, nazovi me odmah.

Ako means if. It introduces a condition:

• Ako ti zatreba pomoć = If you need help
• nazovi me odmah = call me immediately

So the whole sentence has the structure If X happens, do Y.

In Croatian, when a subordinate clause comes before the main clause, it is normally separated by a comma.

So:

• Ako ti zatreba pomoć, = conditional clause
• nazovi me odmah. = main clause

This is very standard punctuation in Croatian.

Zatreba is a verb form from zatrebati, a perfective verb related to trebati.

Here it means something like:

• if you come to need
• if you end up needing
• if you happen to need

It is 3rd person singular present, but with a perfective verb after ako, Croatian often uses this form to talk about a future possibility.

So Ako ti zatreba pomoć is naturally understood as If you need help / If help becomes necessary for you.

This is one of the most useful distinctions in Croatian.

• Ako ti treba pomoć = If you need help / If you are in need of help
  This can sound more general or ongoing.
• Ako ti zatreba pomoć = If you happen to need help / If you come to need help
  This points more to a possible future situation.

So zatreba fits very well when offering help for some future moment.

Ti is the unstressed dative form of ti = to you.

So:

• ti zatreba pomoć literally means help becomes necessary to you
• more naturally: you need help

Croatian often expresses need with a dative person:

• Treba mi pomoć. = I need help.
• Treba ti pomoć. = You need help.

So ti is in the dative case.

Pomoć is the noun help, and here it is in the nominative/accusative singular form, which happens to look the same.

In this construction, learners often expect a different ending, but pomoć is one of those feminine nouns whose form does not visibly change here.

You can simply learn the chunk:

• trebati / zatrebati + dative person + noun
• Treba mi pomoć.
• Ako ti zatreba pomoć...

So pomoć stays pomoć.

Nazovi is the imperative of nazvati = to call.

So nazovi! means:

• call!
• give a call!

Because the sentence is speaking to one person informally, Croatian uses the singular informal imperative:

• nazovi me = call me

Me is the short, unstressed form of I/me in the accusative.

• nazovi me = call me

Croatian often uses short clitic forms like me, te, ga, je, nas, vas, im in normal sentences.

The longer form mene is used for emphasis, contrast, or after certain prepositions:

• Nazovi mene, ne njega. = Call me, not him.

So in a neutral sentence, me is the natural choice.

Odmah means immediately / right away.

In this sentence:

• nazovi me odmah = call me immediately

Its position here is very natural. Croatian word order is flexible, but this is the most neutral placement.

You may also hear variants depending on emphasis, but nazovi me odmah is the standard, everyday version.

Croatian has fairly flexible word order, but some elements prefer certain positions.

In particular, short unstressed words like ti and me are clitics, and they usually appear near the beginning of their clause.

So:

• Ako ti zatreba pomoć sounds natural
• Nazovi me odmah sounds natural

You could change word order in some contexts, but the version here is the most neutral and idiomatic.

Yes, this sentence is informal singular. It is addressed to one person you would say ti to.

Informal singular:

• Ako ti zatreba pomoć, nazovi me odmah.

Polite or plural:

• Ako vam zatreba pomoć, nazovite me odmah.

Changes:

• ti → vam
• nazovi → nazovite

Yes, you might hear something like that, and it is understandable, but it is less neat and less idiomatic in this kind of short offer.

Croatian often prefers:

• Ako ti zatreba pomoć... or
• Ako ti treba pomoć...

Instead of building it with će in this sentence. The original version sounds very natural and compact.

It sounds natural, friendly, and helpful. It is a straightforward offer of support:

• not overly formal
• not dramatic
• very common in everyday Croatian

It is the kind of thing you would say to a friend, colleague, classmate, or family member:

• Ako ti zatreba pomoć, nazovi me odmah. = If you need help, call me right away.