Ako večera počinje kasnije, mogu sada da pijem čaj.

Ako means if. It introduces a conditional clause.

In this sentence, Ako večera počinje kasnije sets up the condition, and mogu sada da pijem čaj gives the result.

A useful thing to remember is that Serbian often uses the present tense after ako, even in situations where English learners might expect something more future-like.

Here, večera is a noun meaning dinner or supper.

You can tell because it is the subject of počinje:

• večera počinje = dinner starts

It is not a verb here. The verb related to eating dinner would be večerati.

Počinje is the 3rd person singular present form, matching večera, which is singular.

So:

• večera = dinner
• počinje = starts / is starting / begins

Serbian verbs have endings that show person and number, so počinje tells you the subject is he/she/it or a singular noun like večera.

This is an aspect question.

• počinje comes from the imperfective verb počinjati
• počne comes from the perfective verb početi

Very roughly:

• počinje focuses more on the process or a regular/planned situation
• počne focuses more on the single completed starting point

In a sentence like this, počinje sounds natural if you are talking about a schedule or timing in a general way.

You may also hear Ako večera počne kasnije..., which is also possible, but it has a slightly different feel.

Kasnije means later.

It is the comparative form of kasno, which means late.

So:

• kasno = late
• kasnije = later

Serbian can use kasnije by itself, without saying exactly later than what, if that comparison is already understood from context.

Because Serbian often leaves out subject pronouns when they are not needed.

Mogu already means I can, because the verb ending shows 1st person singular.

So:

• mogu = I can
• ja mogu = I can, with extra emphasis or contrast

If you add ja, it usually sounds more emphatic, like:

• Ja mogu, ali on ne može. = I can, but he can’t.

After many verbs, especially modal verbs like moći = can, Serbian very often uses:

da + present tense

So:

• mogu da pijem = I can drink

This is one of the most common Serbian patterns and is completely normal.

You may sometimes see an infinitive in Serbian, but da + present is extremely common and often preferred in everyday language.

Pijem is the 1st person singular present of piti, meaning to drink.

So:

• piti = to drink
• pijem = I drink / I am drinking

After da, the form still looks like an ordinary present tense form, but in meaning it often works like an English infinitive:

• mogu da pijem = I can drink

It can mean either, depending on context.

Serbian does not have a separate mandatory progressive form like English I am drinking. The present tense often covers both:

• I drink
• I am drinking

Here, because of mogu and sada, the meaning is closer to I can drink now.

Because čaj is the direct object of pijem, so it is in the accusative case.

For masculine inanimate singular nouns, the accusative is the same as the nominative.

So:

• nominative: čaj
• accusative: čaj

That is why the form does not change.

Yes. Serbian word order is fairly flexible.

The given sentence has a neutral, natural order:

• Ako večera počinje kasnije, mogu sada da pijem čaj.

But other versions are possible, for example:

• Ako večera počinje kasnije, mogu da pijem čaj sada.
• Mogu sada da pijem čaj ako večera počinje kasnije.

The meaning stays similar, but the emphasis can shift slightly.

Because the sentence starts with a subordinate clause:

• Ako večera počinje kasnije

Then comes the main clause:

• mogu sada da pijem čaj

In Serbian, it is normal to put a comma between them when the ako clause comes first.

Yes. Both mean now.

• sada is a bit fuller
• sad is shorter and very common in everyday speech

So this is also natural:

• Ako večera počinje kasnije, mogu sad da pijem čaj.

Yes, this is another aspect choice.

• pijem is imperfective: it focuses on the activity of drinking
• popijem is perfective: it often suggests drink up, finish drinking, or have a whole drink

So:

• mogu da pijem čaj = I can drink tea
• mogu da popijem čaj = I can drink a tea / finish a tea / have a cup of tea

Both can work, but they are not exactly the same. The sentence you were given uses pijem, which is the broader, less bounded option.