Javiću ti se večeras.

Literally, it is something like:

• javiću = I will contact / I will let know
• ti = to you
• se = part of the verb javiti se
• večeras = tonight / this evening

A natural English translation is usually:

• I’ll contact you tonight
• I’ll get in touch with you tonight
• sometimes I’ll let you know tonight, depending on context

So the sentence is not necessarily about a phone call only. It often means I’ll reach out to you tonight in a general sense.

Javiću is the 1st person singular future form: I will contact / I will get in touch.

It comes from the verb javiti (se).

In Serbian, the future can be formed with ću, ćeš, će, ćemo, ćete, će plus the infinitive. But when the auxiliary is attached to the verb, it is written as one word:

• ja ću se javiti = I will contact / get in touch
• javiću se = same meaning, just the contracted written form

With verbs ending in -ti, the -ti drops before the future ending:

• javiti → javi-
• javi + ću → javiću

So javiću is basically I will ... built directly onto the verb stem.

Because the verb here is javiti se, not just javiti.

This is very important:

• javiti = to inform, to announce, to let someone know something
• javiti se = to get in touch, to check in, to contact, to speak up, to report oneself

In this sentence, se is part of the meaning of the verb. Without it, the sentence would mean something different.

Compare:

• Javiću ti. = I’ll let you know.
• Javiću ti se. = I’ll contact you / I’ll get in touch with you.

So se is not optional here.

Ti is the dative clitic meaning to you.

So:

• javiti se nekome = to get in touch with someone
• ti = to you

That is why the sentence does not use a direct object like English you. Serbian uses the dative here.

Compare:

• Javiću ti se. = I’ll contact you.
• literally: I’ll get in touch to you / I’ll report myself to you

That literal English sounds unnatural, but it helps explain the grammar.

Yes, Serbian word order is flexible, but not completely free.

This sentence is natural as:

• Javiću ti se večeras.

You could also hear:

• Večeras ću ti se javiti.
• Ja ću ti se javiti večeras.
• Ti ću se javiti večeras. — not correct

A key point is that short unstressed words like ću, ti, se are clitics, and they usually go in a special position, often near the beginning of the clause.

That is why forms like these are common:

• Ja ću ti se javiti večeras.
• Večeras ću ti se javiti.

And also the contracted version:

• Javiću ti se večeras.

So the sentence you were given is perfectly normal, but Serbian often allows other natural rearrangements depending on emphasis.

Because Serbian often omits subject pronouns when the verb already shows who the subject is.

Javiću already clearly means I will. So ja is not necessary.

You can add ja if you want emphasis:

• Ja ću ti se javiti večeras. = I’ll contact you tonight (with extra emphasis on I)

But in ordinary speech, leaving it out is completely normal.

Not necessarily.

Javiti se is broader than English to call. It can mean:

• to call
• to text
• to message
• to get in touch
• to check in
• to let someone hear from you

So Javiću ti se večeras does not force the meaning I’ll phone you tonight. It usually means something more general like I’ll contact you tonight.

If you want to be specific, Serbian can use other verbs:

• Pozvaću te večeras. = I’ll call you tonight.
• Poslaću ti poruku večeras. = I’ll send you a message tonight.

Večeras means tonight or this evening, depending on context.

It is an adverb, not a noun phrase.

So:

• večeras = tonight / this evening
• sutra = tomorrow
• danas = today

Examples:

• Dolazim večeras. = I’m coming tonight.
• Javiću ti se večeras. = I’ll contact you tonight.

It refers to the evening of today, not just evening in general.

Yes, it matters.

Javiti se is generally perfective, which fits well with a single completed future action:

• Javiću ti se večeras. = I’ll get in touch with you tonight.

The imperfective partner is usually javljati se:

• Javljam ti se svaki dan. = I contact you every day / I check in with you every day.

So:

• javiti se = one completed act of getting in touch
• javljati se = repeated, habitual, or ongoing contacting/checking in

That is why the perfective verb sounds natural in this sentence: it refers to one specific future contact tonight.

This is a very useful distinction.

• Javiću ti. = I’ll let you know.
• Javiću ti se. = I’ll contact you / I’ll get in touch with you.

So:

1. javiti nekome nešto = to tell someone something / let someone know
2. javiti se nekome = to contact someone / get in touch with someone

Examples:

• Javiću ti odgovor sutra. = I’ll let you know the answer tomorrow.
• Javiću ti se sutra. = I’ll get in touch with you tomorrow.

That little se changes the structure and meaning quite a lot.

Yes, you can absolutely say:

• Ja ću ti se javiti večeras.

It is not more correct; it is just a different, equally correct way to form the future.

Serbian commonly has both patterns:

• Ja ću ti se javiti večeras.
• Javiću ti se večeras.

The second one is often more compact and very common in everyday language.

So you should understand both as normal Serbian.