Ja sada čitam knjigu.

Yes, they usually do. In čitam, the ending already tells you the subject is I.

So Ja sada čitam knjigu and Sada čitam knjigu can both mean I am reading a book now.

Including ja often adds emphasis, contrast, or clarity. For example:

• Ja sada čitam knjigu = I am reading a book now
• This can sound like you are stressing that it is you, not someone else

In many everyday situations, Serbian speakers would simply omit ja unless they want emphasis.

Sada means now. It tells you the action is happening at the present moment.

So:

• Čitam knjigu = I read / I am reading a book
• Sada čitam knjigu = I am reading a book now

It helps make the ongoing, current-time meaning clearer.

Čitam is in the present tense.

In Serbian, the present tense can often cover both:

• I read
• I am reading

The time meaning depends on context. In this sentence, sada strongly points to the English am reading meaning.

Because knjigu is the accusative singular form of knjiga.

• knjiga = nominative, the basic dictionary form
• knjigu = accusative, used here because book is the direct object of the verb read

You are reading what?
→ knjigu

This is very common in Serbian: nouns change form depending on their role in the sentence.

Knjigu is in the accusative case.

The accusative is commonly used for the direct object of a verb, especially with verbs that act directly on something.

Here:

• čitam = I read
• knjigu = the thing being read

So the structure is:

• subject: ja
• adverb: sada
• verb: čitam
• direct object: knjigu

Yes. Serbian word order is more flexible than English word order because cases and verb endings carry a lot of grammatical information.

All of these can work, though they may sound slightly different in emphasis:

• Ja sada čitam knjigu
• Sada čitam knjigu
• Knjigu sada čitam
• Čitam knjigu sada

The most neutral and natural versions are usually:

• Sada čitam knjigu
• Ja sada čitam knjigu if you want emphasis on I

Changing the order often changes focus rather than basic meaning.

Yes, čitati is an imperfective verb.

That matters because imperfective verbs are often used for:

• ongoing actions
• repeated actions
• general habits

So čitam works very naturally for I am reading or I read in a general sense.

The perfective partner is usually pročitati, which means something more like to read through / finish reading.

Compare:

• Čitam knjigu = I am reading a book / I read books
• Pročitaću knjigu = I will read the book completely / finish reading it

Both mean now.

• sada is the full form
• sad is a very common shorter conversational form

So you may hear:

• Ja sada čitam knjigu
• Ja sad čitam knjigu

Both are natural. Sad is especially common in everyday speech.

The letter č is pronounced roughly like ch in chocolate, but usually with a firmer, more distinct sound.

So:

• čitam sounds approximately like CHEE-tam

Also:

• c in Serbian is not like English k or s; it sounds like ts
• č is a separate letter from c

Serbian spelling is quite phonetic, so words are usually pronounced much the way they are written.

Serbian has no articles like English a/an and the.

So knjigu can mean:

• a book
• the book

Which one is meant depends on context.

If you need to make it clearer, Serbian usually does that through context, word order, or additional words, not with articles.

Yes, knjiga is a feminine noun.

That affects its case endings. In the singular:

• nominative: knjiga
• accusative: knjigu

For many feminine nouns ending in -a, the accusative singular changes to -u.

So this sentence is also a good example of a very common feminine noun pattern in Serbian.

In strict English, I read a book now sounds unnatural, but Serbian present tense is broader than English.

Without context, čitam can mean either:

• I read
• I am reading

But once you add sada, the most natural English translation is I am reading a book now, because the sentence refers to an action happening at this moment.

So grammatically Serbian uses the present tense, but in English you usually translate it with the present continuous here.