Ako ne razumeš poruku, pročitaj je ponovo.

Ako means if. It introduces the condition:

• Ako ne razumeš poruku = If you don’t understand the message

So the whole sentence has the structure if X, then do Y.

In Serbian, the negative particle ne is usually written as a separate word before the verb:

• razumeš = you understand
• ne razumeš = you do not understand

This is the normal way to negate most verbs in Serbian.

Razumeš is the 2nd person singular present tense of razumeti / razumjeti (to understand).

It means:

• you understand

Because it is 2nd person singular, the sentence is speaking to one person in an informal way, like you in English.

Because poruku is in the accusative case, which is used for the direct object of the verb.

• poruka = message (nominative, dictionary form)
• poruku = message as the thing being understood/read

So:

• razumeš poruku = you understand the message
• pročitaj poruku = read the message

Since message is the object in both parts, Serbian uses poruku.

Pročitaj is the imperative form of pročitati, meaning:

• read
• more literally, read through / finish reading

So pročitaj je ponovo means read it again.

This is the singular informal command form, used when talking to one person.

This is about aspect, which is very important in Serbian.

• čitati = to read (imperfective)
• pročitati = to read through / to finish reading (perfective)

In this sentence, the speaker wants one complete action: read it again. That is why pročitaj is natural here.

Very roughly:

• čitaj = read / be reading / keep reading
• pročitaj = read it completely

Here je means it.

It is the unstressed object pronoun for a feminine singular noun. Since poruka (message) is feminine, the pronoun referring to it is:

• je = it

So:

• pročitaj je = read it

Do not confuse this je with the very common verb form je meaning is. In this sentence, it is clearly a pronoun, not a verb.

Serbian object pronouns like je are clitics, which means they usually cannot stand alone and tend to appear in a special position in the sentence.

In a simple command like this, pročitaj je is the natural order:

• pročitaj je ponovo = read it again

English says read it again, and Serbian works similarly here, though Serbian clitic placement follows its own rules.

Ponovo means again.

So:

• pročitaj je ponovo = read it again

A common near-synonym is opet, which also means again. In many contexts, both work:

• Pročitaj je ponovo.
• Pročitaj je opet.

Both are natural, though ponovo can sometimes sound a little more like once again / anew.

The comma separates the if-clause from the main clause:

• Ako ne razumeš poruku, = If you don’t understand the message,
• pročitaj je ponovo. = read it again.

This is normal punctuation in Serbian, just as in English.

It is informal singular because of the verb forms:

• razumeš
• pročitaj

These are used when speaking to one person with ti.

If you wanted a polite/formal or plural version, you would use forms for vi, for example:

• Ako ne razumete poruku, pročitajte je ponovo.

That can mean either If you don’t understand the message, read it again addressed politely to one person or to several people.

Yes. Serbian usually does not need an explicit subject pronoun when the verb already shows who the subject is.

So there is no need to say ti here, because:

• razumeš already means you understand
• pročitaj already means read! addressed to you

That is why the sentence sounds natural without a separate word for you.