Bilo da pohađam onlajn nastavu, bilo da pohađam nastavu uživo, učim.

It is a set expression meaning whether ... or ....

So the structure:

bilo da pohađam onlajn nastavu, bilo da pohađam nastavu uživo, učim

works like:

whether I attend online classes or attend classes in person, I study / learn

It introduces two alternatives, and the main clause shows that the result stays the same in either case.

Great question. Here bilo is part of the fixed expression bilo da, so you should not read it as the ordinary past-tense form of biti (to be).

In other words, in this sentence:

• bilo da functions as a conjunction-like expression
• it does not mean it was that

So learners should recognize bilo da ... bilo da ... as one chunk with the meaning whether ... or ....

Because each part that follows is a full clause with a conjugated verb:

• da pohađam
• da pohađam

In Serbian, bilo da is the normal pattern when you follow it with a verb clause.

Compare:

• bilo da učim, bilo da radim = whether I study or work
• bilo onlajn, bilo uživo = whether online or in person

In the second example, there is no full verb clause, so da is not needed.

Because Serbian often likes clear parallel structure in expressions like this.

So:

• bilo da pohađam onlajn nastavu, bilo da pohađam nastavu uživo

sounds balanced and explicit.

You can shorten it, though. For example:

• Bilo da pohađam onlajn nastavu ili nastavu uživo, učim.

That is also natural. The version with repetition is just more symmetrical and a bit more formal or rhetorical.

Pohađam comes from pohađati, which means to attend in the sense of regularly attending:

• school
• classes
• a course
• lessons

So it is more specific than simply go.

For example:

• Pohađam kurs srpskog. = I attend a Serbian course.
• Idem na kurs srpskog. = I go to a Serbian course.

Both can work, but pohađati sounds more like formal attendance.

Because pohađati takes a direct object, and that object is in the accusative case.

The basic form is:

• nastava = nominative

But after pohađati, it becomes:

• nastavu = accusative singular

So:

• pohađam nastavu = I attend classes / instruction

This is a very common pattern in Serbian: the verb takes an object, and that object changes case.

In Serbian, nastava is often used as a collective or uncountable idea meaning instruction / classes / teaching in general.

So even though English may prefer a plural in many contexts, Serbian very naturally uses singular:

• Imam nastavu. = I have classes.
• Pohađam nastavu. = I attend classes.

This is normal and idiomatic.

They are related, but not the same.

• nastava = teaching / classes / instruction in general
• čas = one class period, one lesson

So:

• Pohađam nastavu. = I attend classes / instruction.
• Imam čas u deset. = I have a class at ten.

In this sentence, nastava is the better choice because it refers to the mode of instruction as a whole: online vs in person.

Uživo literally often means live, but in this context it means in person, face-to-face, or onsite.

So:

• nastava uživo = in-person classes

It is an adverb and does not change form.

You will also see uživo in other contexts:

• gledati prenos uživo = watch a live broadcast
• videti nekoga uživo = see someone in person

Yes. Onlajn is very common in modern Serbian.

It is basically the Serbian-spelled version of online, and it is widely used in everyday language:

• onlajn nastava
• onlajn kurs
• onlajn sastanak

It usually behaves as an indeclinable modifier, so it does not change form here.

You may also see online written in its English spelling, especially in branding or informal writing, but onlajn is perfectly normal Serbian spelling.

Because Serbian present tense can express:

• a general truth
• a habit
• an ongoing action

Here it expresses a general fact:

No matter which kind of classes I attend, I study / learn.

So učim is not necessarily right this second I am studying. It can simply mean I study or I am learning in general.

It can mean all of those, depending on context.

The verb učiti has a fairly wide range:

• učim srpski = I study Serbian / I am learning Serbian
• učim za ispit = I am studying for an exam
• učim nešto novo = I am learning something new

In this sentence, because the topic is nastava, English often prefers I study or I am learning.

Both are first person singular, present tense:

• pohađam = I attend
• učim = I study / learn

Serbian usually drops the pronoun ja because the verb ending already tells you who the subject is.

So:

• Ja pohađam nastavu.
• Pohađam nastavu.

Both mean the same thing, but the second is more typical unless you want emphasis.

The commas separate the paired bilo da ... bilo da ... parts from each other and from the main clause.

The structure is:

• alternative 1
• alternative 2
• main result

So the punctuation reflects the logic of the sentence:

whether X, whether Y, Z

That is why the sentence is written:

Bilo da pohađam onlajn nastavu, bilo da pohađam nastavu uživo, učim.

Yes. Here are some natural alternatives:

• Bilo da pohađam onlajn nastavu ili nastavu uživo, učim.
• Bilo onlajn, bilo uživo, učim.
• Bez obzira na to da li pohađam onlajn nastavu ili nastavu uživo, učim.

All of these are grammatical. The original version is just nicely balanced and very clear.

Not completely, but the given word order is very natural.

Putting the bilo da ... bilo da ... structure first makes the contrast come first, and then učim gives the main point at the end.

That is stylistically effective in Serbian.

You could rearrange things, but the original sentence sounds smoother than something like:

• Učim bilo da pohađam onlajn nastavu, bilo da pohađam nastavu uživo.

That version is understandable, but less elegant.