Sigurno ćemo stići na vrijeme.

Ćemo is the 1st person plural form of the auxiliary verb htjeti when it is used to make the future tense.

So:

• ćemo = we will
• stići = arrive

Together, ćemo stići means we will arrive.

In Croatian, the future tense is often formed like this:

• future auxiliary
  • infinitive

So:

• ja ću doći = I will come
• mi ćemo stići = we will arrive

Croatian often leaves out subject pronouns when they are not needed, because the verb form already shows who the subject is.

Here, ćemo already tells you the subject is we.

So both of these are possible:

• Sigurno ćemo stići na vrijeme.
• Mi ćemo sigurno stići na vrijeme.

The version without mi is more natural unless you want extra emphasis on we.

Here sigurno means certainly, surely, or definitely.

In this sentence, it expresses confidence:

• Sigurno ćemo stići na vrijeme. = We’ll definitely arrive on time.

Be careful: sigurno can also sometimes relate to the idea of safety in other contexts, because it comes from siguran = sure / safe / certain, depending on context.

Croatian word order is fairly flexible, and putting sigurno first gives it a natural emphasis.

So:

• Sigurno ćemo stići na vrijeme.
• Stići ćemo sigurno na vrijeme.
• Mi ćemo sigurno stići na vrijeme.

These are all possible, though they may sound slightly different in emphasis. Starting with sigurno sounds natural if you want to stress certainty right away.

Yes. Stići means to arrive, to get there, or sometimes to manage to reach a place or time.

In this sentence, it means to arrive.

A useful thing to know is that stići is a perfective verb. That means it usually refers to a completed result: actually arriving.

That is why it works very naturally in the future here:

• ćemo stići = we will arrive / we will make it

Because after the future auxiliary ćemo, Croatian normally uses the infinitive of the main verb.

So:

• ćemo stići = we will arrive
• ćemo doći = we will come
• ćemo vidjeti = we will see

The infinitive here is stići.

Na vrijeme literally looks like on time / at the proper time, and that is exactly how it is used.

It means:

• on time
• in time, depending on context

In this sentence, it most naturally means on time.

Examples:

• Došao je na vrijeme. = He arrived on time.
• Moraš krenuti na vrijeme. = You have to leave in time / on time.

Yes, very much so. It is a common expression meaning on time or in time.

You should learn it as a chunk:

• na vrijeme

Even though you can analyze the words separately, learners usually benefit from remembering it as one set phrase.

Croatian has a group of words called clitics, and ćemo is one of them in this use. Clitics tend to appear in the second position in a clause.

That helps explain why this sentence is:

• Sigurno ćemo stići na vrijeme.

and not usually:

• Sigurno stići ćemo na vrijeme. ❌

So once sigurno takes the first position, ćemo naturally comes right after it.

Yes. Stići ćemo na vrijeme is also completely correct and very common.

In fact, with many verbs in the future tense, Croatian allows both patterns:

• ćemo stići
• stići ćemo

But when another word like sigurno comes first, the clitic ćemo usually goes right after that first element:

• Sigurno ćemo stići na vrijeme.

Yes: both contain ć, which is a Croatian consonant different from plain c and also different from č.

For learners, the main thing is:

• c is like ts
• č is a harder ch
• ć is a softer ch-like sound

So in:

• ćemo
• stići

the ć is the softer one.

You do not need perfect pronunciation immediately, but it is worth noticing the difference because Croatian spelling is very consistent.

Not in the basic sense of this sentence. Sigurno mainly expresses certainty, not probability.

So this sentence means something like:

• We will definitely arrive on time.

If you wanted probably, Croatian would more naturally use words like:

• vjerojatno = probably

Compare:

• Sigurno ćemo stići na vrijeme. = We will definitely arrive on time.
• Vjerojatno ćemo stići na vrijeme. = We will probably arrive on time.

Here vrijeme is in the accusative, but this is one of those expressions where the form looks the same as the nominative.

• nominative: vrijeme
• accusative: vrijeme

With na, Croatian can use different cases depending on meaning, but in the expression na vrijeme, you should mainly just learn the whole phrase as a standard idiom meaning on time.