Moram da platim košulju i pantalone danas.

In Serbian, a very common way to express must + verb is:

• morati + da + present tense

So:

• Moram da platim = I have to pay / I must pay

This is the most natural everyday pattern in Serbian.

You may also see moram platiti, but moram da platim is much more common in standard everyday Serbian.

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

• platiti / platim = perfective
  • focuses on the action as completed
  • to pay off / to pay completely
• plaćati / plaćam = imperfective
  • focuses on the process, repetition, or habit
  • to be paying / to pay regularly

In this sentence, the speaker means they need to complete the payment today, so the perfective verb is natural:

• Moram da platim... danas. = I need to pay ... today (finish the payment today)

If you used plaćam, it would sound more like:

• I am paying
• I usually pay
• or it would focus more on the ongoing action rather than completion.

Serbian often drops subject pronouns when they are clear from the verb ending.

• moram already means I must
• so ja is usually unnecessary

Compare:

• Moram da platim... = I must pay...
• Ja moram da platim... = I must pay... (extra emphasis)

So the sentence without ja is perfectly normal and natural.

Because it is the direct object of the verb platiti, so it goes into the accusative case.

The noun is:

• košulja = shirt (nominative)

In the accusative singular, feminine nouns ending in -a usually change to -u:

• košulja → košulju

So:

• platim košulju = pay for the shirt

This is a very common pattern:

• knjiga → knjigu
• torba → torbu
• haljina → haljinu

Because pantalone is a plural noun, and in this sentence it is an inanimate direct object.

For inanimate plural nouns, the accusative plural is usually the same as the nominative plural.

So:

• pantalone (nominative plural)
• pantalone (accusative plural)

That is why it does not visibly change here.

Also, pantalone is normally used only in the plural, like pants/trousers in English.

Because that is simply how these nouns work.

• košulja = shirt → a normal singular noun
• pantalone = pants/trousers → normally a plural noun

So Serbian treats pantalone much like English treats pants:

• singular idea in meaning, but plural in form

Examples:

• Nove pantalone su skupe. = The new pants are expensive.
• Kupio sam pantalone. = I bought pants.

You would not normally use a singular form like pantalona to mean one pair of pants in everyday Serbian.

In Serbian, platiti can directly take the thing you are paying for as an object.

So:

• platiti košulju literally looks like pay the shirt but actually means
• pay for the shirt

This is normal Serbian usage.

You can think of it as:

• platiti nešto = pay for something

So no extra word like for is required here.

Because Serbian does not have articles like English a/an/the.

So:

• košulja can mean a shirt or the shirt
• pantalone can mean pants, some pants, or the pants

The exact meaning depends on context.

In this sentence:

• košulju i pantalone could mean
  • a shirt and pants
  • the shirt and the pants

Both are possible depending on the situation.

Yes. Serbian word order is fairly flexible, and danas can move depending on emphasis.

The original sentence:

• Moram da platim košulju i pantalone danas.

Other natural possibilities include:

• Danas moram da platim košulju i pantalone.
• Moram danas da platim košulju i pantalone.

All of these are understandable.

Often:

• Danas moram... emphasizes today
• Moram danas... also highlights today
• ... danas can sound a little more neutral or like an afterthought

The most natural version many speakers would probably use is:

• Danas moram da platim košulju i pantalone.

But the original sentence is still correct.

The dictionary form is:

• morati = must / have to

Its present tense forms are:

• ja moram = I must
• ti moraš = you must
• on/ona/ono mora = he/she/it must
• mi moramo = we must
• vi morate = you must
• oni/one/ona moraju = they must

So moram is simply the 1st person singular present form.

Yes, it is grammatical and understandable.

A more natural everyday word order for many speakers might be:

• Danas moram da platim košulju i pantalone.

That said, the original sentence is fine. The main thing learners should notice is:

• moram da + verb
• the accusative košulju
• the unchanged plural pantalone
• the use of perfective platim

So the sentence is a good, natural example of several important Serbian patterns.