Na internetu često čitam poruke.

Na internetu is the usual Serbian way to say on the internet. Even though English also uses on, the important thing in Serbian is that na is simply the standard preposition here.

After na meaning location, Serbian uses the locative case, so internet becomes internetu:

• internet → basic dictionary form
• na internetu → on the internet

This is similar to other location phrases such as:

• na stolu = on the table
• na poslu = at work / at the workplace

So in this sentence, na internetu is a fixed, natural location expression.

Internetu is in the locative singular.

The noun is internet (masculine). After na when it means in/on/at a location, Serbian normally uses the locative:

• internet → nominative
• na internetu → locative

So the pattern is:

• na + locative for location
• na + accusative for movement toward something

For example:

• Sam na internetu. = I am on the internet.
• Idem na internet. = I am going onto the internet.
  This second one is less common in everyday speech than the location phrase, but it shows the case contrast.

Često is an adverb, and it means often.

It tells you how frequently the action happens:

• čitam = I read / I am reading
• često čitam = I often read

Its position is fairly flexible, but some placements sound more natural than others. In your sentence:

• Na internetu često čitam poruke.

this sounds perfectly natural.

You could also hear:

• Često čitam poruke na internetu.
• Poruke često čitam na internetu.

The meaning stays very similar, but the word order can shift the emphasis. Serbian word order is more flexible than English word order.

In Serbian, the subject pronoun is often left out because the verb ending already shows who is doing the action.

Čitam is the 1st person singular present tense form of čitati:

• čitam = I read / I am reading

Because the ending -am already tells you it is I, Serbian usually does not need ja.

So:

• Čitam poruke. = I read messages.
• Ja čitam poruke. = I read messages.

The version with ja is possible, but it adds emphasis, for example if you want to contrast yourself with someone else:

• Ja čitam poruke, a on piše odgovore. = I read messages, and he writes replies.

The infinitive is čitati, meaning to read.

Čitam is the present tense, 1st person singular form. A basic present-tense pattern is:

• ja čitam = I read
• ti čitaš = you read
• on/ona/ono čita = he/she/it reads
• mi čitamo = we read
• vi čitate = you read
• oni/one/ona čitaju = they read

So in the sentence, čitam specifically means I read.

Poruke is the accusative plural of poruka.

The noun poruka means message. Since the sentence talks about reading messages in the plural, Serbian uses the plural direct object form:

• poruka = message
• poruke = messages

Because poruke is the direct object of čitam, it is in the accusative case. For this noun, the nominative plural and accusative plural happen to look the same:

• poruke = nominative plural
• poruke = accusative plural

So the form is correct for I read messages.

Yes. Poruka is a feminine noun.

You can usually recognize many feminine nouns because they end in -a in the dictionary form:

• poruka = message
• knjiga = book
• škola = school

In this sentence, its plural object form is poruke.

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

Čitati is an imperfective verb. It is used for:

• repeated actions
• habits
• ongoing actions
• general activity

That fits well with često = often, because often suggests repetition or habit.

So:

• često čitam poruke = I often read messages

If you used pročitati, that would be perfective, meaning something more like read through / finish reading a message or messages as a completed action. Perfective verbs generally do not work naturally with adverbs like često when the meaning is habitual in the same way.

So čitati is the natural choice here.

Yes. Serbian word order is relatively flexible.

The sentence:

• Na internetu često čitam poruke.

is natural and emphasizes the setting on the internet early in the sentence.

Other possible orders include:

• Često čitam poruke na internetu.
• Čitam poruke često na internetu.
• Poruke često čitam na internetu.

Not all versions are equally neutral. Some sound more marked or emphasize a different part of the sentence. The original sentence is a very normal, natural order.

A useful general idea is:

• the meaning is carried a lot by case endings
• word order often helps express focus or emphasis

It can mean either, depending on context.

The Serbian present tense often covers both:

• I read
• I am reading

In this sentence, because of često = often, the meaning is clearly habitual:

• I often read messages on the internet

So here it is not really I am reading right now, but rather something you do regularly.

It would be:

• Ja na internetu često čitam poruke.

or more naturally in many contexts:

• Ja često čitam poruke na internetu.

This is grammatically fine, but ja is usually unnecessary unless you want emphasis or contrast.

For example:

• Ja često čitam poruke na internetu, ali ne pišem često odgovore.
  = I often read messages on the internet, but I do not often write replies.

Without special emphasis, Serbian normally leaves ja out.

The letter č is pronounced roughly like ch in church, but usually with a firmer, harder sound than in English.

So:

• često
• čitam

both begin with that ch-like sound.

This is different from ć, which is another Serbian letter and has a softer sound. English speakers often mix up č and ć at first, so it is good to notice that čitam and često both use č, not ć.